Difference between Contextual User and Accessing User?

AccessingUser =>  User currently logged in
Contextual =>  Varies, but generally a user represented by some content, usually the user of a profile page you are viewing.

So if you are logged in as UserA  and looking at UserB's profile,  UserA is the accessing user, UserB is contextual.  Does that help a bit?

That does help, thanks. Outside of the profile page example, I'm struggling to think of other examples where contextual user would come into play. But I'm new at this, so it'll come eventually. Thanks for the response!

Contextual is really what drives the concept of "Current" in the script/widget apis.  So another example would be a blog post.  It has a contextual user that represents the author.  Same applies to a gallery post, or a thread.  So that means in the script/widget Api when on the post or thread page calling the following will result in getting the author:

#set($author = $core_v2_user.Current)

Its far more common to use contextual groups or applications than users outside of a profile.  So for a blog post page, calling current on the group Api gives the blog's parent group, calling current on the blog give the post's blog:

  

#set($currentGroup = $core_v2_group.Current)
#set($currentBlog = $core_v2_blog.Current)

Contextual is really what drives the concept of "Current" in the script/widget apis.  So another example would be a blog post.  It has a contextual user that represents the author.  Same applies to a gallery post, or a thread.  So that means in the script/widget Api when on the post or thread page calling the following will result in getting the author:

#set($author = $core_v2_user.Current)

Its far more common to use contextual groups or applications than users outside of a profile.  So for a blog post page, calling current on the group Api gives the blog's parent group, calling current on the blog give the post's blog:

  

#set($currentGroup = $core_v2_group.Current)
#set($currentBlog = $core_v2_blog.Current)