o micron literally means "small o" and o mega literally means "big o", but those computer scientists, when they use "big O notation" they write it with an O. Omega is sad :(

There's also a "big omega", which gives a lower bound instead of an upper bound. I guess the name is a little redundant, though.

To be fair, big O and little o have different meanings in asymptotic notation, and I guess it doesn't pronounce as well as "big omicron" and "little omicron". (Although Ω and ω are both used as well.)

Is that how it's pronounce? Letter O + micron like size? My first read was ohm eh cron, like the job

They are greek letters. Letter o/O is omicron, ω/Ω is omega (the last letter of the greek alphabet).

Omicron = o + mikron = small o Omega = o + mega = big o

cool! thanks!

I always thought "big Ο" was uppercase omicron. That would make it consistent with Θ and Ω.