An Accepted Solution is a post that the author of the thread or the Community Crew has deemed the most accurate response to their question. It also serves as a time saver; when searching the Community for answers and falling upon an Accepted Solution, you know it’s tried, tested, and true.
In a nutshell, accepting a solution helps the Community find answers more quickly, and with less hassle. So when a fellow community member provides the correct answer or solution to your post, make sure to accept it as the solution so that future viewers of the thread can see your stamp of approval.
The Accept as Solution button can be found right above the reply button (when you’re logged in)
This is what it looks like when a thread has an accepted Solution:
As you can see, the accepted solution is floated to the top and embedded in the original poster's (OP’s) post.
When browsing a board, you can also see which thread has an accepted solution thanks to the solution/checkmark icons:
Note: There can only be one accepted solution per thread, and just as with all other interactions, you have to be signed in to accept a solution.