This is a stub and may end up being a page rather than a blog post…
Apps and platforms – there are different ways of viewing Twitter and tweeting. On any browser you can use desktop Twitter by typing https://twitter.com into the address bar, but on smartphones and tablets it’s usually easier to use an app (many are free, downloadable from the Apple app store or Android store). What you see on the resulting ‘page’ can depend on the app or the device. Just because something is the case on App X doesn’t mean it’s the case on App Y or Device B. See also third party apps.
Currently I tend to use desktop Twitter on Firefox and Echofon for iPhone when on the move.
Address, link and URL – these all mean more or less the same thing but it’s dull writing the same one every time. On Twitter these all appear as clickable links (typically in blue text but it will depend on your settings) and, by default, have a length of 22 characters (and allow +1 for a space) whether or not the link is longer or shorter than that. This means that if you type http://is.gd (an URL shortener which itself has only 12 characters +1 for a space) in a tweet Twitter will treat it as if it’s 22 characters long, but a genuinely long URL will still only have 22 characters assigned to it.
Avatar – fancy word for profile pic. It just means a representation of you, but in digital space.
Desktop Twitter – what you’re using if you’re reading Twitter via a web browser (eg Firefox, Internet Explorer) and can see something like https://twitter.com in the address bar. While mobile (phone and tablets) apps are probably used more, currently desktop Twitter is where you can do all the heavy lifting on Twitter (searching further back in time, amending your account information etc).
Live-tweeting – tweeting / reporting in real-time from an event (eg a conference). Ideally adding a bit of context and explaining what’s going on rather than just capturing sound-bites, but some of those are fun too.
Third party apps – any app used to access Twitter on any device (including a mobile phone or tablet as well as computers) that isn’t created or owned by Twitter. This includes things like Echofon or Janetter for phones etc, or Tweetdeck for computer browsers. I think it’s important to be aware that these can behave differently (show different things) from ‘native’ Twitter-owned apps such as ‘Twitter for iPhone’. If someone blocks you you’ll still see their tweets if you’re using Echofon but you won’t if you’re using Twitter for iPhone. This has led a lot of people to infer, wrongly, that blocking someone means they don’t see your tweets.
See Can you stop someone from seeing your tweets? for more info on blocking someone and what happens if you make your account private.
Reverse image search – [I might move this to another section]. If an account seems suspicious you can use Google Images or Tin Eye to search for the image in their avatar / profile pic (or in a tweet). This involves dragging and dropping the image into the search bar and seeing other pages on the internet where that image has been used (or stolen from).