my name is Terry but why people call me Ter?

people call you Ter because of their laziness,
for Americans, they used to call people's name by short form
for examples:
they call Jason for Jay
Johnson for John
David for Dave
all of the short form just have one vowel
that makes more easy to call

that's your friend call you in short-form. for example:-
andrew - andy
lawrance - larry
terence - terry
nicholas - nick
joseph - joe
etc.

its just a short form to call you, most people call u ur name in a short form because they are friend or are ur close friends
my name is teresa and my friends call me ter as wel!

May be people think they call you Ter is better than call you Terry.My answer is not ture you have to ask you friend about this question.May be they can help you.