Show a term description when the search filter in a view is that term? I have a content type that has several vocabularies. Nodes can have 0, 1, 2 or all 3 terms selected.   

Ive added a field to the terms so they all have a description as well as their name. 

Color (vocabulary)

-Red (term)
  --This has red items (term description) 

-Blue (term)
  --This has blue items (term description) 

-Green (term)
  --This has green items (term description) 

Pattern (vocabulary)

-Stripy (term)
--This has stripy items (term description) 

-Spotted (term)
--This has spotty items (term description) 

-Pinstripe (term)
--This has pinstriped items (term description) 

I have a View of nodes of the content type. I'm using Better Exposed Filters so you can filter by the different terms. I need it so when you have selected a single term its description is shown at the top of the view. 

So if you checked 'Red' and 'Stripy', or 'Blue' 'Spotted' and 'Pinstripe', then no description would be shown. But if you just checked 'Blue' then 'This has blue items' would be printed at the top of the view before the nodes tagged with 'Blue' were listed.
Create a template for the view.

Edit the view. Under "Advanced" find "Theme: Information". Click on it to find the names of the templates that are applied in your theme. I think "Display output" is what you want to use. It will show you the contents of the template.

In your custom theme, create a template with the same name as the template you copied. Paste in the contents of the template you copied.

Now you can use PHP to get the information you want (available variables are listed in the comments of the templates), manipulate it as needed, and add it to the $header or wherever you want it, without any PHP in the database.