conjunction
used to introduce another choice or possibility
used in negative statements to introduce something else that is also true
used to say what will happen if a specified thing is not done
used to introduce another number or amount that is possibly the correct one
used to introduce the reason why something said previously is true
a - used to introduce a word or phrase that defines or explains what another word or phrase means
b - used to introduce a word or phrase that corrects or states more precisely something you have just said
or else
or so