What's the Difference Between "Keyword Related" & "Partly Keyword" Related Sites?

I see this option and wondering how they differ? 

Surely you either use a keyword to find a site or you don't? 

Can someone explain this in a little more detail and maybe provide an example (a search query) as to how it differs? 

partly means that this engine is using your keywords only sometimes (1/10 of every query) in the hope to get new results with it. The darker green colored engines use the keyword always, yellow colored use it never.

Thanks.

What happens when you select a platform with "partly uses keywords" and then under options select

1) Always USE keywords to find target sites.

2) DO NOT set a number for "xx" keywords must be present" / disable this option.

Does it then use the platforms with "partly uses keyword" or does it ignore these then?

That option will use a keyword even on the yellow colored sites. It uses a keyword any time.

What happens to the platforms that don't use a keyword to be found? Does it force these to use a keyword as well? 

(Sorry for all the comments, but travelling and spending the last 3 days catching up and setting it up for the next while. Also lost a few good rankings so just rechecking a number of things, which is causing a few questions!) 

yes it will use a keyword on every search engines query...EVERY