ledg·er /ˈlejər/
a book or other collection of financial accounts of a particular type
There are a few ways to hold onto your cryptocurrency. You can keep it on a software wallet. Which can sometimes be deprecated when you forget you've got an altcoin stored there, and noooooow it's locked.
You can keep it on an exchange. But, that's not always the best thing to do. Actually, it's the worst. See this list.
It's not 100% hackproof, but the better alternative is a hardware wallet. When you do that, you lose the convenience of knowing what your cryptocurrency is currently valued at. It is the very thing that the emotional state of FUD and FOMO cannot exist without.
Insert ledger. Your... sorta offline cryptocurrency companion. If you've got a cryptocurrency in AirDrop limbo, track it. If you need to keep an eye on the market cap of a former 💩coin turned volatile social media trend, track it.