Final answer:
Bursae are fibrous sacs filled with synovial fluid that prevent friction between tendons and bones. They reduce friction by separating the adjacent structures, preventing them from rubbing directly against each other.
Step-by-step explanation:
The fibrous sacs filled with synovial fluid found in areas where friction from tendons occurs are called bursae. Bursae are fluid-filled sacs that serve to prevent friction between skin, muscle, or tendon and an underlying bone. They reduce friction by separating the adjacent structures, preventing them from rubbing directly against each other.