The space C at top is a connected space. The space D at bottom is disconnected.
<ul><li><a href="//commons.wikimedia.org/wiki/File:Connected_and_disconnected_spaces.svg" title="File:Connected and disconnected spaces.svg">Connected and disconnected spaces.svg</a>: by <a href="//commons.wikimedia.org/wiki/User:Caesura" title="User:Caesura">Caesura</a> / derivative work: <a href="//commons.wikimedia.org/wiki/User:Qniemiec" title="User:Qniemiec">Qniemiec</a> (<a href="//commons.wikimedia.org/wiki/User_talk:Qniemiec" title="User talk:Qniemiec">talk</a>)</li></ul>
<a href="//commons.wikimedia.org/wiki/File:Connected_and_disconnected_spaces.svg" title="File:Connected and disconnected spaces.svg">Connected and disconnected spaces.svg</a>