Most musicians know about or have at least heard of midi, midi is a form of digital signals sent from one piece of equipment to another, a good analogy would be to consider a piano keyboard being like a row of switches either pressed on or off. There is other information included in this switching information like how hard you pressed the switch(velocity) and for how long it is held down(length), popular music software allows you to record yourself pressing these switches and then replay them.
Once the information is recorded it can be manipulated to play with different timings, strengths, lengths or use different sounds, so in the studio Midi is widely used to record drum loops, piano, string sections again the list is endless usually from a Master keyboard, you are probably going to use some kind of Computer based system (who doesn’t’ in these days?) in your Studio, whether it’s a PC or Mac you will probably need a Midi patch bay and a Midi signal splitter/ booster box to send a copy of the Midi signal you have recorded to several rack mounted pieces of kit/ Synth modules/ effects etc. at the same time.
If you try to daisy chain the signal using “Midi through” from one Unit to the next, Delays in the signal can get introduced and you find units at the end of the chain sometimes not responding or having a delay or other unwanted effects happen
Electronic piano keyboards usually have Midi included into them these days and a studio will usually have one where the keys are “weighted” to give the feel of a real Piano, however Midi has or had when I last checked only around 128 different velocity points for each note. That is to say apart from Volume (which is kind of the same thing, and also has 128 variable levels one of which is usually set for all the keys) you can only strike a note 128 different ways!
So there is a difference between the feel and sound level/ tone of a real Piano but not many people have room for them and you can’t easily sync what you play on a real piano with modern electronic formats without having a Midi conversion done on the Piano, or trying to use software to recognize what has been played and covert it to Midi in a modern sequencing/ Recording Software package.
Other types of Midi controllers can operate and store EQ positions and levels on Modern Mixing desk’s along with which digital effects to call up and effect amounts, even routing Patch bays without the need to unplug a single Jack!. Although Modern Computer Softwarepackages are now including digital on screen versions of all these functions down to including Inserting, Mixing, EQ’ing, Patching, adding effects to Audio recordings, and playing Midi Sounds with effects all at the same time practically all from one box!.