The terms "masculine" and "feminine" rhymes have nothing to do with biological gender, but instead are terms derived from the rhythmic patterns associated with grammatical gender in romance languages.
In English, the dominant poetic meter used for the sonnet is iambic pentameter, i.e. lines consisting of five iambic feet. An iamb consists of a weak syllable followed by a strong syllable. Thus in most cases, the rhyme words in a sonnet end with strong syllables, a pattern known as "masculine rhyme". An example from "Pied Beauty" would be:
Glory be to God for dappled things—
Fresh-firecoal chestnut-falls; finches’ wings;
In feminine rhyme, a extra-metrical weak syllable is appended to the line, and the rhyme sound includes both the preceding strong and the extra weak syllable, e.g. the internal rhyme fallow/cow. The main rhyme words in this poem though are all masculine rhymes.