Sentence:  This is the <WSD>CheckUser</WSD> software, accessible to a restricted number of admins. <WSD>CheckUser</WSD> identifies what IP address registered Wikipedians are accessing the site from. 
Meaning of the word marked with <WSD> tags:  A tool that allows someone to view the IP addresses of wiki users, so as to identify sock puppets, etc; or the authority to use that tool.