Normally refers to "I/O operations" (I/O bound operations) that are relatively slow (compared to the speed of the processor and the RAM memory):
the data from the client to be sent through the network
the data sent by your program to be received by the client through the network
the contents of a file in the disk to be read by the system and given to your program
the contents your program gave to the system to be written to disk
a remote API operation
a database operation to finish
a database query to return the results
CPU bound
Audio or image processing.
Computer vision: an image is composed of millions of pixels, each pixel has 3 values / colors, processing that normally requires computing something on those pixels, all at the same time.
Machine Learning: it normally requires lots of "matrix" and "vector" multiplications. Think of a huge spreadsheet with numbers and multiplying all of them together at the same time.
Deep Learning: this is a sub-field of Machine Learning, so, the same applies. It's just that there is not a single spreadsheet of numbers to multiply, but a huge set of them, and in many cases, you use a special processor to build and / or use those models.