Because we must read so much, it’s rare for you or me to come across a word we don’t know. I suppose there are at least three reasons we might: the word is old, obsolete; it’s a jargon word, proper to some trade or art we don’t practice; or it’s slang from a crowd we don’t hang with (such as young people, for example). All three explain “ligger”.
I came across it in a recent novel, used as a slang term originating in the British music scene that, according to the Urban Dictionary, means among other things:
. . . [more] “The Friday Fillip: “All That Is the Kinge’s Stuffe””