what is a uke and a seme??

its not necessarily "smaller and weaker" and "bigger and stronger" (although many times that is the case). its Mehr like (and correct me guys if this sounds off cause i suck at explaining) the seme is the dominate one in the relationship and the uke is the opposite (and Von opposite i do not mean necessarily submissive because many times theyre not..).

Sorta..Uke would be the girl an Seme would be the guy in a boy X boy relationship, if I'm not mistaken :)

Not necessarily; the "Seme" is simply the Dominant one in the Relationship and the "Uke" is the Submissive one.

the uke is typically the weaker and smaller. the seme, is taller and stronger(typically) and has a duty to protect the uke! :D
hope i helped u!

I'm not the best at explaining but I would say that the Uke is the one that "receives" and the Seme is the one that "gives". At least, that's how I think about it.

The words uke and seme come from the Japanese words 受ける(ukeru) and 攻める(semeru), which mean "to recieve" and "to attack" respectively. Basically, the attacker (seme) makes romantic advances and is the dominating partner during sex, while the receiver (uke) is just the object of the seme's affections.

At least, that's how it goes in typical BL archetypes.