To clear things a little more and to be a bit specific on details... ie the technical side of things.
First... this is not an airplane subject, it's a transmitter/receiver subject although airplanes do have these... but so do other RC vehicles. So technically it's an electronics subject.
A 2.4Ghz transmitter can typically bind to many receivers if they are compatible but how many depends on which brand and model of transmitter you are asking about. There is no standard on this. Cheap transmitters found coming with most toy grade vehicles usually don't have this option, it's only when you get into the hobby grade equipment that it may be an option.
Receivers on the other hand are only bound to one transmitter... period. Assuming you are talking about any of the current typical 2.4Ghz radio equipment... other types like those used before the point in time that 2.4Ghz was starting to be used... did not have that limitation only if you tried to have multiple transmitters on at the same time with the problem that trying to do that would usually result in a crash or uncontrollable vehicle since the receiver had no way to ensure which signal it was suppose to listen to.
Compatibility between brands will depend on a lot of factors. Spectrum will typically only work with their own compatible ( DSM / DSMX ) receivers, Futaba has its own compatibility etc. There are also generic radios that can handle multiple methods to connect/bind together. So you have to know what type of 2.4Ghz connection your radio and receiver is compatible with.
As Keith ( Admiral ) stated.... there is an option on most radios to allow master and a slave radio to used together. This is typically referred to a buddy box setup or trainer setup and how it's done again, is depending on which make and model you are doing this with.