bladder infection vs urinary tract infection (uti)

Basically, a bladder infection is an infection of the bladder. A urinary tract infection can be situated anywhere along the waterworks, AKA the urinary tract, hence the term urinary tract infection. And that could be anywhere from the urethra, up to the bladder, to the uteters, and right up to the kidneys (by which time the person will be in an awful lot of discomfort). 

But basically, if you notice symptoms like pelvic pain, pain urinating, burning while peeing, having to pee all the time but not being able to empty your bladder, etc, it is time for a doctor who can diagnose which part of your urinary tract is affected.