As should be painfully obvious to anyone with even a passing knowledge of the English language, a "layabout" is a lazy person. Literally, someone who lies around all day, without doing anything.
Interestingly, this word seems to be a case of bad grammar, appearing to make the common error of mistakenly substituting the transitive verb "to lay" for the intransitive verb "to lie." Most likely this is merely a case of nonstandard usage, although it is perhaps distantly possible that the word is simply in the past tense.
The term "layabout" first emerged in Great Britain during the Great Depression, as a derogatory term for unemployed loafers.
Today, the term still remains chiefly a Britishism, and is almost unrecorded in non-jocular native English speech outside of the British Isles.