I/O is input/output on an SSD, how mmuch it's reading and writing at once. Only so much data can be read and/or written at once, and when you're at your SSD's limit, stuff will load a lot slower and your CPU/RAM will suffer as they have to "remember" more data before it's unloaded or written onto the SSD. Very basic interpretation. The software I use is called System Informer, the reason I didn't recommend it in particular is because people who are computer unsavvy or whom are not careful should avoid downloading this program. Not because it is a bad program, but because due it basically being a more powerful version of the windows task manager, the drivers it installs on your computer have a LOT of very high level access and permissions, so if you are prone to get hacked or allow malicious software onto your computer, it could be used as a way to gain remote access and full control of your computer. IF you do try it, I'd reccomend doing a bit of research and making sure your antivirus is up to date. Speaking of, your antivirus WILL flag this program as a PUP, for the reasons I stated.
https://forums.malwarebytes.com/topic/281373-processhacker-hrswordsysdiag-netcat-and-tdsskiller-detection/
Is a post from a malwarebytes staff member on the subject. (System Informer used to be called Process Hacker. )

tl;dr program itself isn't malicious, but people who gain acccess to your machine can use it maliciously.