Hi @carol_a_johnson 
Welcome to the Canvas Community. It depends on where you are seeing this icon, but assuming it is on the Assignments page in your Canvas course, it sounds like you are teaching a course that is based upon a blueprint course, where material was "pushed out" into your course site from a blueprint master. This is explained here: https://community.canvaslms.com/docs/DOC-11662-4152759004 , and you can see some illustrations of what the locked icon means. It also means that certain things are uneditable in that quiz, but exactly what--and to what extent--is determined by how the content was locked. Check the information under the View Locked Object and Edit Locked Object headings in that online documentation. You will also want to check in with (perhaps) your local chair or coordinator for your department/school/institution regarding this, since course blueprint masters are usually managed by someone else in the department.
I hope this provides a bit of an explanation; if NOT, a screen capture would help, so long as no student names are included.
