“Sapphic” is an umbrella term for any women or female-aligned nonbinaries who are attracted to women/female-aligned nonbinaries. For example, lesbians, bi women, and demigirls attracted to other demigirls could all consider themselves sapphic. The term is derived from the Greek poet Sappho; her sexuality is highly debated, but from her poems it is clear that she liked women. Here is a sample verse from her Hymn to Venus.
O Venus, beauty of the skies, To whom a thousand temples rise, Gayly false in gentle smiles, Full of love-perplexing wiles, O goddess! from my heart remove The wasting cares and pains of love.