What do you call...

[TiggerToo]

.....the pastic or rubber cover which protects a electric connector (male/female)?

 

[Poignard]

A boot

https://www.bing.com/images/search?q=terminal+boots&FORM=HDRSC2

 

[pvb]

Or a sheath, sleeve, insulator, etc

 

[Alex_Blackwood]

.....the pastic or rubber cover which protects a electric connector (male/female)?

Shroud!

 

[TiggerToo]

A boot

https://www.bing.com/images/search?q=terminal+boots&FORM=HDRSC2

Cheers! That's it

 

[Topcat47]

On my boat they're almost all shrink-wrap.

 

[macd]

Cheers! That's it

There's no hard-and-fast convention about it, but "boot" is commonly used for larger items, such as those pictured, which are commonly found on batteries, windlass motor connectors, and the like. 12V Planet calls the same things "Push-On Terminal Covers", which is a bit of a mouthful.