A 'loop' in a control system is one where the output may (or may not) have an influence on the input the most common type of loops in control are 'Closed Loop', 'Open Loop', 'Feedback Loop'.
2. Computer Programming
A 'loop' in a computer program is where the instructions within the loop are repeated over and over again until some condition is met that stops the loop.
For example a typical software loop looks something like this
For x = 1 to 10 Print x Next
The loop prints x, 10 times.
An 'infinite' loop is one that cannot end and is normally a mistake on the part of the programmer. For example, the loop below will never end because x keeps getting reset to 1
For x = 1 to 10 Print x x = 1 Next