So, here's what these words mean, succintly:
This is the catch-all word. Pingbacks and trackbacks (and refbacks) are all linkbacks. Each of them offers a way to let the author of content published on the web (say, at a website or a blog) know when someone else has linked to their content.
Linked? As in "hyperlinked." Someone, somewhere has read what you've placed on the web, and they've taken the time to link to that content in their post, article, or other form of website content. For an example, I'm linking here to Wikipedia's definition of linkback, which I've found helpful in writing this paragraph, and which provides more details on linkbacking if you wish to go there and learn more.