What does 50/50 mean?

[Epithet Lost]

I see it a lot but the tekkenzaibatsu site's notation page does not offer explanation on it.
thanks,

[Shuten Doji]

It essentially means a mixup

[rikiohipman]

A kind of mixup, that gives a player effectively 2 offensive options, which can't be defended against both at the same time, thus giving the player a 50% chance of successful hit in case of proper execution.

[Рафнсвартр]

basically it's a mind-game. You can't block it on reaction, so you need to guess. For example, the guy hits you with his middle punch and then goes for the low\high or middle and you need to guess right and punish him (not sure if all 50'50's of Tekken are punishable though) or get punished.