4T stand for 4 - Toddler. So, usually if a child is 4 years of age they would wear a 4T, just like a 2 year old would wear a 2T. However, there are always exceptions to that rule--some children grow at different rates so it isn't uncommon to be one year behind or ahead in clothing. For instance, my cousin was 3 years old, and wore 2T in most shirts because she was so petite; but she had to wear 4T pants (we'd have to take them in) sometimes because she was tall and had long legs, so she needed the length of the 4T. Also, every clothing brand determines their sizes a little differently--some use weight, others use height/length measurements. I'd recommend taking the child with you if you're intending to purchase clothing for them...if that's not an option, include the receipt for mom and dad just in case!
