Your question it too general to answer.
Look in the link I will make below to learn about AT&T
t is the significance of Z-transform
It depends on what the variables x and t represent.
The constant "t" in an equation represents time, and its significance lies in determining how the variables in the equation change over time.
A. T. Cross Company was created in 1846.
The population of A. T. Cross Company is 930.
A. T. Cross Company's population is 2,010.
T. Marzetti Company's population is 3,100.
T. Marzetti Company was created in 1896.
No. T-Mobile is a Private limited company.
what size company is At&t
H. T. Hackney Company was created in 1891.
H. T. Hackney Company's population is 3,400.