Optiboot (an older version) is installed by default on the Arduino Uno and (as of 2018) official Arduino Nano boards. It can be installed on all older mega8, 168 or 328 based Arduinos. As of 2019, ...
CSV means comma separated values. It's like a normal "txt" file with commas at regular places to separate some values. Typically the first line of CSV file is a "header", containing names of columns ...