恣 is a bound form (b.f.) that never appears alone in modern Mandarin. It combines with other characters to form compounds meaning 'unrestrained', 'indulgent', or 'doing as one pleases'. You'll see it in literary or formal contexts, such as 恣意 (zìyì, 'wanton/unrestrained') and 恣情 (zìqíng, 'indulge oneself'). It carries a slightly negative connotation of excessive freedom or lack of discipline.