A crash cart used to be a literal cart in the datacenter with a monitor and keyboard to plug into a rack-mounted server to recover access. Not sure if there is something more modern now.
Still is that where I work. Doesn't help if you need serial console access, for that you'll need a laptop and a USB/serial dongle, or an actual old school serial terminal such as a VT100, VT220, etc.
In a previous life, I and a biz partner ran a web company on about 5 servers. We cabled the serial ports together in a daisy chain, used serial port consoles, and had software running on every system to access the ports. This way, if a system died, you just had to ssh into the system connected to it and you had access to the failed system's console. These were Supermicro servers, so the pre-boot screens and all that were also available. It came in very handy and saved us lots of trips to Hurricane Electric.
A computer on a movable cart that is correctly provisioned to get direct access to a server in a rack in a datacenter. Nowadays just an appropriate laptop on a desk with casters.