The non-breaking space looks like a normal space, but prevents an automatic line-break from occurring between the two text items it connects.
Wikipedia link: Non-breaking space
I use it when I want words not to get separated from their inline bullet-type markers [(i), a), – etc.] This is useful in grant application documents where you might want to use lists but space is at a premium.
To type a non-breaking space:
Windows: Alt+255
Mac: Option+Space