That’s the entire purpose of FCC regulations, capturing what it means to the FCC. No more and no less.
Fixed stations are radios in fixed locations that may only transmit analog signals directly to each other, using no more than 15 watts output power. They are allowed to transmit on either the 462 MHz main channels or the 467 MHz main channels. They may be operated by remote control.
I just added that last sentence, but it’s important because it allows a fixed station under direct control to communicate to another fixed station which you are remotely controlling. Thus, a pair of fixed stations, using audio tones, could be used to control an irrigation system or detect and report various alarm conditions, etc, similar to a very basic SCADA system.
Or it could be used to form a full duplex intercom system.
Or anything else that you can conceive of that can be done using full or half duplex, audio only with 15 watts.
It’s really up to you. FCC simply put some limitations on.