It's just a naming convention. You can call it anything you want. Same goes with color coding, convention lang din. In fact, pwede ka gumawa ng sarili as long as yung SEND-RECEIVE ends (pins 2 and 6) are correct.
What are their uses?
Straightthrough. Kung yung 2 devices are on different layers of OSI, eg Layer2 and Layer3 such as connection between a switch and a PC. Or, PC-to-router/gateway.
Crossover. Kung yung 2 devices are on the same Layer, eg PC-to-PC. Or PC-to-router/gateway.
Modern devices normally autodetect via automdix, so hindi na strictly required yung cable ends to match. Pero, kung magagawa, mas ideal pa din yung be explicit with the connection.