An abbreviation is a shortened form of a word.

app

application (as in ‘mobile application’ for phones)
Ms.

Miss
approx

approximately
n.b.

note (nota bene)
blog

web log
no.

number
e.g.

for example (exampli gratia)
op

operation
est.

established
stat

statim (= immediately)
etc.

etcetera (= and so on)
tbsp

tablespoon
frat

fraternity (often used for university fraternities that party, rather than more serious fraternities)
temp

temporary
ID

identification
tsp

teaspoon
i.e.

that is (Latin term ‘id est’)
vet

veteran
misc.

miscellaneous
vet

veterinarian
Mr.

Mister
vs.
versus
Mrs.

Mistress (however Mrs is pronounced ‘missus’)