With reference to problem solving, fixation refers to 

Problem-solving is the act of defining a problem; determining the cause of the problem; identifying, prioritizing, and selecting alternatives for a solution; and implementing a solution.

There are 4 steps to solve the problem:

Step 1: Understand the problem.

Step 2: Devise a plan (translate).

Step 3: Carry out the plan (solve).

Step 4: Look back (check and interpret).

Fixation - Inability to see a problem from a fresh perspective. This impedes problem-solving, Two examples of fixation are mental set and functional fixedness.