A full charge cycle is full discharge -> recharge. See: http://support.apple.com/en-gb/HT201585

A battery has a limited number of them but you should do it once a week or so because they don't like to be stuck on full charge all the time. You can get the battery replaced anyway (probably costs same price as the laptop :P I joke..).

Yeah GPU and CPU usage can get quite high with jQuery and 1080/4k videos. More so in fullscreen. I have a little app that tells me when it's switching to the other GPU so I can tell when it's under load.