A contraction of 'there is' or 'there are', commonly used in spoken and informal written English.
A combination of the adverb 'there' (from Old English 'thær') and the verb 'is' (from Old English 'beon'). The apostrophe was historically used to mark omitted letters, though modern informal usage often drops it. This contraction became standard in casual speech.
Technically, 'there's' (with an apostrophe) should only be used with singular nouns, but in real speech, people use it for both singular and plural all the time—'there's people everywhere!' Language rules are more like suggestions that actual speakers bend.
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