Homongi or houmongi directly means "visiting wear" - (homon = visit + gi= wear). It is charactherized by the colorful decorations that run continously over the seams on the shoulders and the sleeves and this is the most elaborate kimono for married women and the second most for unmarried women. The homongi takes over the role of furisode when she marries and is her semi-formal kimono. Wearing homongi was spread widely as a special go-out-dress for the upper-class ladies in Meiji era.
Homongi can be worn at parties or weddings by (not close) relatives and friends of the bride couple. It ranks lower than the tomesode and furisode and slightly higher than it's close relatives, tsukesage and komon.
It is often made of Chirimen(crepe), Rinzu, Mon-Isyo and the beautiful decorations are painted on the kimoni with the yuzen technique and/or embroidered. The length of the sleeves varies, unmarried women wear with longer sleeves. Homongi is usually worn with a fukuro obi with matching obi-age and obi-jime.
They can be worn by both married and unmarried women, and is less formal than the homongi. It is regarded as informal, unless it has a crest in the back. The pattern of a tsukesage are less obvious, and spreads over a smaller area, mainly below the waistline. the name derives from the way the patterns are dyed. The sort of go upwards to from the left hem to the right shoulder.
If you ask me, I sometimes have a hard time distinguishing between homongi and tsukesage, and they can be very similar. But if you se a colorful, widely spread decorations that run over the seams (like the one above here), then you can be pretty sure that it's a homongi, and vice versa, if you see a modestly patterned kimono, with the excact same small decoration on the right sleeve and shoulder (like the one on the left), then you can be pretty sure that it is a tsukesage.
Both the pink homongi and the pink tsukesage is from www.yamatoku.jp/classic