Do you know what it is?
Ransomware, which holds your files for 'ransom', is a very real threat. When a computer becomes infected/compromised with ransomware, it begins to encrypt the files so no one can access them without paying a fee. Once the files have been encrypted, ransomware then displays a message about how you, supposedly, can gain access to your files by paying a ransom. There is no guarantee paying the ransom will allow you to regain access to those files.