Western, mainland Malaysia
Peninsular Malaysia, historically known as Malaya, also known as West Malaysia or the "Malaysian Peninsula", is the western part of Malaysia that comprises the southern part of the Malay Peninsula on Mainland Southeast Asia and the nearby islands. Its area totals approximately , which is nearly 40% of the total area of the country; the other 60% is in East Malaysia on the island of Borneo.
It shares a land border with Thailand to the north and a maritime border with Singapore to the south. Across the Strait of Malacca to the west lies the island of Sumatra, and across the South China Sea to the east lie the Natuna Islands of Indonesia. At its southern tip, across the Strait of Johor, lies the island country of Singapore. Most of Peninsular Malaysia's interior is forested, mountainous and rural; the majority of Malaysia's population and economy are concentrated on the coastal western half, which is where the country's prominent urban areas are located.
States and federal territories.
Peninsular Malaysia consists of 11 out of the 13 states, and two out of the three federal territories of Malaysia, which includes the national capital of Kuala Lumpur. The states are listed as the following:
 *Two federal territories are embedded within Selangor, which are Kuala Lumpur and Putrajaya.
Etymology.
Originally comprising the states and territories of the Federation of Malaya, the then Federation under the Malaysia Agreement merged with the Crown Colony of North Borneo, the Crown Colony of Sarawak, and the self-governing State of Singapore to form the new Federation called Malaysia. The merger was initially proposed in order to reunify Singapore with its hinterland in the Federation as they were originally associated under British Malaya but later separated and were governed separately after the formation of the Malayan Union. Even when the Malayan Union transformed into the Federation of Malaya, Singapore was not a part of it. Although politically distinct, Malaya was then seen geographically as comprising the States of the Federation of Malaya in the Peninsula and Singapore. In order to facilitate the merger, the Borneo States (which initially also included Brunei) were brought in as well as it was believed that with the inclusion of the various ethnic groups in Borneo, the racial arithmetic would be offset such that the influx of ethnic Chinese from Singapore would not politically overwhelm Malaya, satisfying the Malay ultras. 
Ultimately, both Malaysia and Singapore agreed that after a merger, Singapore would retain autonomy in labour, education and health, among others, unlike the other states in the Federation of Malaya. In exchange, Singapore received an underproportioned representation in the House of Representatives of Parliament. Singapore within Malaysia was seen as having a special status (similar to Northern Ireland in the United Kingdom) and was thus not grouped with the other non-autonomous states in the Peninsula. Although this arrangement was brief and Singapore was ultimately expelled from the Federation two years later in 1965, becoming a fully sovereign country, the Interpretation Act 1965 of the Parliament of Singapore still defines Malaya as comprising the States of Malaya and Singapore in a geographical sense. Today, the States of Malaya are colloquially referred to as Peninsular Malaysia and West Malaysia, excluding the Borneo States and Singapore. The term should also not be confused with the Malay Peninsula, which includes lands that are a part of Myanmar and Thailand.
Terminology.
Peninsular Malaysia (States of Malaya) comprises the states of Johor, Kedah, Kelantan, Malacca, Negeri Sembilan, Pahang, Penang, Perak, Perlis, Selangor, and Terengganu, as well as the federal territories of Kuala Lumpur and Putrajaya.
Malaya comprises Peninsular Malaysia and the Republic of Singapore.
Malay Peninsula comprises the southern tip of Myanmar, Peninsular Malaysia, and Southern Thailand.
Demographics.
Ethnicity in Peninsular Malaysia (2020)
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The majority of people in Peninsular Malaysia are ethnic Malays, predominantly Muslims. Large Chinese and Indian populations exist. The Orang Asli are the indigenous people of Peninsular Malaysia; in 2022, they numbered around 209,575 and mostly lived in inland parts of the region.
Economy.
As of 2012, Peninsular Malaysia oil production stood at 520,000 barrel of oil equivalent per day.
Other features.
East Coast and West Coast.
The term "East Coast" (; Jawi: ڤنتاي تيمور) is particularly used in Malaysia to describe the following states in Peninsular Malaysia facing the South China Sea, a marginal sea of the Pacific Ocean:
The term "West Coast" (; Jawi: ڤنتاي بارت) refers informally to a collection of states in Peninsular Malaysia situated towards the western coast generally facing the Strait of Malacca which is a component of the Indian Ocean, as opposed to the East Coast. The West Coast is partitioned further into three regions:
Although Johor has a coastline facing the South China Sea on the Pacific Ocean, it is not generally regarded as an East Coast state, since the main coastline of the state is located on the Straits of Johor of the Indian Ocean.
The East Coast of Peninsular Malaysia is socioculturally different in terms of overall racial composition and political affiliations compared to the West Coast – the states' demographics in the former are overwhelmingly Malay and its people lean towards social conservative and Islamist values, their electoral representation dominated by the Malaysian Islamic Party.
West Malaysia and East Malaysia.
The distinction between West and East Malaysia (Sabah and Sarawak) goes beyond the sphere of geography. Being separate regions administratively before the formation of the Malaysia, there exists more autonomy than the original States of Malaya, e.g. in having a different judicial court structure and separate immigration regulations. These rights were granted as part of Sarawak's 18-point agreement and Sabah's 20-point agreement with the Federation of Malaya during the formation of expanded federation.
Notes.
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References.
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External links.
 Media related to at Wikimedia Commons