What is the difference between Shonen'ai, JUNE, Yaoi and Boys' love? The difference between Shonen'ai and Yaoi as already been asked. 

However, I encountered a few more terminologies concerning anime and mangas referring to masculine homosexuality :


Shōnen'ai
JUNE
Yaoi
Boys' love


What are the main differences between those genres?
Shounen-Ai 
Literally translated means boys love. However, in these type of series, it usually represents an innocent, non sexual nature of homosexuality.
Ex- 7-Ghosts.

(Taken from wikipedia)


  The term shōnen-ai (boy love) originally connoted ephebophilia or pederasty in Japan, but from the early 1970s to the late 1980s, was used to describe a new genre of shōjo manga, primarily produced by the Year 24 Group of women authors, about beautiful boys in love. Characteristics of shōnen-ai include exoticism, often taking place in Europe, and idealism. Jeffrey Angles particularly notes Moto Hagio's The Heart of Thomas (1974) and Keiko Takemiya's Kaze to Ki no Uta (1976-1984) as being groundbreaking, noting their portrayal of intense friendship between males, including jealousy and desire.


June- This name actually comes from a specific manga magazine and it cannot be said as a genre or demographic per se.

(From Wikipedia)


  A manga or text story with male homosexual themes for women written in an aesthetic (耽美 tanbi) style, named for the Juné magazine.


Yaoi


  Yaoi (/ˈjaʊi/, Japanese: [ja.o.i]), also known as Boys' Love (BL), is a Japanese genre of fictional media focusing on romantic or sexual relationships between male characters, typically aimed at a female audience and usually created by female authors. Although yaoi is typically aimed at a female audience, the genre also attracts some male readers; however, manga aimed at a gay male audience (bara) is considered a separate genre.


Boys Love

Yaoi and Boys-Love are basically the same thing and can be used interchangeably