I don’t know if .slim.js is a standard name extension for javascript library, but for jQuery, it is a build without some extensions, just check the beginning of the file:
-ajax,-ajax/jsonp,-ajax/load,-ajax/parseJSON,-ajax/parseXML,-ajax/script,-ajax/var/location,-ajax/var/nonce,-ajax/var/rquery,-ajax/xhr,-manipulation/_evalUrl,-event/ajax,-effects,-effects/Tween,-effects/animatedSelector,-deprecated
Typically you have no ajax support (jQuery.ajax is not defined), no effects, and the deprecated method are removed.
Concerning requireJS, as far as I know if you require jquery, the only file “included” will be jquery.js, so you would have to explicitely require jquery.slim in order to get jquery.slim.js file included, which is not what you want.