Question: I think there should be a specific term for someone getting a free ride without consent, but I keep thinking of the word "hijack" which clearly isn't correct.

Examples include jumping on a train without a ticket, or riding without consent on the back of a truck. Or perhaps I want to sit in on someone else's meeting and just observe.

Am I gatecrashing? Or going along for a free ride?

Equally, if I hop on the roof of a train to get somewhere for free, is there a term for that?

Answer: 
**Free Rider** — [M-W](http://www.merriam-webster.com/thesaurus/free+rider)

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> *n.* a person who is supported by or seeks support from another without making an adequate return
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> *"claimed that welfare recipients were a bunch of free riders with little or nothing to offer society"*
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> ***Synonyms*** bloodsucker, freeloader, leech, hanger-on, moocher, parasite, sponge, sponger
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This is not a travel metaphor, but in college we would call that an **audit**. You can **audit** a class which means you attend the class, but you don't get a grade or credit on your transcript.