What does it mean? Understanding what Blake meant by Female Love is a vital key to the meaning of Blake's poetry and pictures; the same thing is true for the more general case, love (he only used the word 782 times!). What did he mean??
It helps when you realize that unlike the great majority of members of the Enlightenment Age, Blake's vocabulary was informed by millennia of intellectual tradition, dating back to the pre Socratic age and earlier ones from Egyptian and Asian cultures. These ideas were subjects of contempt and ignorance to his neighbors--as are ours for that matter. But not for Blake; for him they were his bread and butter, the stuff of life. Once you understand that about Blake you're in a position to query 'female love' without outraged feministic feelings.
So what did he mean? In the ancient traditions (the perennial philosophy) masculine is active, feminine passive, with a masculine sky God and a feminine Earth Goddess. In another pair masculine and feminine relate to thinking and feeling; this came down in Blake to Urizen and Luvah, and more like 'common English' in Jung's two similar functions.
In Blake's system we find the two in their fallen state. In the beginning of his myth we meet among others Urizen (who presumes to be God and is actually the Prince of Light), and Luvah who gets possession of the Sun (symbol of Light) so that he acts as Prince of Light.
If this sufficiently confuses you go on. (As Blake said, 'if the fool would persist in his folly he would become wise'.) MHH, Plate 7, (E 36)
Many of Blake's poems need to be translated into 'common English' in order to grasp what love meant for Blake. However Blake's love meant different things at different times as he went through life. Near the end of his career he got around to using 'common English' with "I've a Wife I love & that loves me" (Notebook; Erdman 481). But in earlier days the word meant several things very different from his mutual love to and from his wife.
Love, like all things, has contrary senses, in fact many senses--for example an ironic sense: speaking of something very repulsive: "Oh I just love that". Blake's love was generally not quite ironic; it was more like 'sick love', The Clod and the Pebble give us a basic introduction into two contrary uses of 'love'.
He used love in a more innocent way with The Little Black Boy which ends with: "And be like him [the white boy], and he will then love me" (Songs of Innocence; Erdman 9).
The Torments of Love and Jealousy, the subtitle of The Four Zoas, is an entirely different matter: selfish love, Love as Power, control, and much such unpleasant reality appears over and over in The Four Zoas.
Wisely or not Blake called that 'female love'.It was embodied in some unsavory women like:
Rahab, (taken from the Bible), the biblical Rahab had more character than the Blakean one. Blake used Rahab as a symbol for a fallen Jerusalem.
Tirzah, ('what have I to do with thee"); this of course is a direct quote from John 2:4; traditionally the mother concerns physical well being while the father represents spirit.
(The fallen) Vala: In Erdman's plate 32 of Jerusalem you will see a shadowed Vala on the left side of the picture. She represents all of the sick kinds of love, such as the Net of Religion (Urizen, plate 25.22 Erdman 82).
Taken together all of these symbols are exemplars of female love:
"Till I turn from Female Love
And root up the Infernal Grove
I shall never worthy be
To Step into Eternity
Let us agree to give up Love
And root up the infernal grove
Then shall we return & see
the worlds of happy Eternity"
All in all love was a bad word for Blake,
although occasionally as we've seen he slipped back into the language of Zion. But 'female love' represents those kinds of 'bad love' that we've mentioned.