Proximity attacks depend on the distance between the user and the opponent to active the specific version. An example would be Ibuki's light punch, that has a version that she attacks with her elbow when the opponent is close by and extends her hand for the further version.
Proximity attacks tend to (but not always) have different Frame Data. Ibuki's close and far LP both have a three frame startup, but others like Poison's close and far HP are vastly different than each others. Poison's close hard punch in Street Fighter X Tekken has a six frame startup and can be Canceled. Conversely her far HP has a 14 frame startup and can not be special canceled at all. Some Target Combos also depend on proximity. Ibuki's Target Combo 4 depends on her close LP, while her Target Combo 5 needs her far LP to activate while both share the same initial followup. Proximity attacks are mostly removed in Street Fighter V with Target Combos like Shinten not having a minimum or maxiumum distance to activate.