According to Wikipedia: “In mathematics and computer science, an algorithm is a finite sequence of well-defined, computer-implementable instructions, typically to solve a class of problems or to perform a computation.”
In general terms these are the list of rules or a sequence to solve a problem. They need to have the steps in the right order so as to get a solution. A good algorithm is an algorithm which not necessarily includes computer code. Instead, the algorithm has to be written in such a way that it can be used in different programming languages.
To gain a better understanding you may watch the video below.