A Performance is MODX's lingo for what was once called a "patch". A Performance is a collection of settings that determines what happens when you strike keyboard piano keys or send MIDI commands. A Performance is made up of one or more PARTs - defining which samples are used. What, if any, arpeggios are used and how those work. How motion sequence/control, if used, interacts. Splits. Layering. MIDI settings such as filtering controllers or which channels to send for each PART (and more).

A Performance is not, in its own right, dealing with defining musical notes. It defines IF you "play" certain notes - then how the synth will respond to those notes.

This: https://www.yamahasynth.com/montage-category/mastering-montage-modx-pattern-sequencer-features
... goes into detail about what a pattern and song is.

Patterns are generally smaller sections of notes/MIDI data that can be chained together and/or looped. A song is more-or-less a "finished" collection of notes/MIDI data that starts and ends and that's it. Yes - you can loop a song - but you don't chain songs. Note that you can use a song as a way to build a pattern. You can create a pattern that uses a song in its entirety - or you can choose select measures from a song to construct a pattern. You can "flatten" a pattern chain into a song. So there's an ability to go both ways (song to pattern, pattern to song).

From the above link:

Patterns are MIDI data and can be used to construct tracks for a Song; They can be used in a variety of ways – you are invited to find your favorite use. You can move data in either direction between the linear Song and the looping Pattern. If you have recorded a long jam to a linear Song, you might use the Pattern feature to work on specific areas of your performance. You might build your Song by creating several musical Pattern sections, then chaining them in a specific play order. How you use the Performance Recorder is really up to you. It is a creative tool.

The Patterns are assembled on the 8 SCENE buttons. Each of the eight SCENEs can be a different section of a composition or you can use each as a complete composition. That is for you to decide. All of the 8 Pattern SCENEs will share the same Tempo, however. Tempo is stored in the Performance.

Each of the 128 Patterns offers loop-based recording that contains 8 segments (Scenes) that can be from 1 to 256 Measures in length.
“Loop” Record can be set to OFF; “Key On Start” is available; Useful for when recording with Arpeggio Phrases.
The “Length” and “Time Signature” are set prior to record – these determine when the Pattern cycles to the top and/or when recording will stop.
Each of the eight SCENE buttons house a set of 16 MIDI Tracks.
Each of the possible 128 Patterns can be created and linked to a specific Performance and/or to a Performance in a LIVE SET.
Implications: The Length setting (1-256 measures) means that these Pattern Scenes can be musical sections, or entire compositions, as you may require. Arpeggio data can be recorded to a Pattern Track allowing you to then “Append”, or otherwise change it to suit your needs. Data recorded to a Pattern Track can be used to create your own custom Arpeggio data.

Sorry I am confused. What is relation among song and pattern and performance ?

A MODX Performance is an assemblage of instruments. As many as 16 can be in “the band”. If you think of the Performance as a band, this will make sense.
Each Part is a member (instrument) of the band.

Song (MIDI) is used as the common language definition — a linear musical composition. Significantly, once started it plays from beginning to end. From Measure 1 until it completes all measures at which point it stops.

A Pattern, however, loops. They are musical sections, (Scene). These sections can be set to a certain number of measures (1-256) at which point it cycles back to the top (and loops endlessly). A musical section in popular music could be an Intro, a Verse, a Chorus, the Bridge, an Interlude, Adagio, etc., etc. Patterns are designed to be a ‘construction tool’. Often when rehearsing a composition, musicians will work on one section at a time — they will play it again and again, over and over during practice. Then when running down the entire composition, they will merge the sections into one continuous entity.

Pattern is where you construct the composition a musical section at a time. (In the MODX, you have a Pattern Chain function — Chaining the sections in a specific playback order then converting it into a ‘finished’ linear Song)

The same Performance (band) can play many different Songs and Patterns (titles).

Say I create a Performance with the following instrument Parts:
Real Drums 1 — Part 1
Upright Bass — Part 2
CFX Stage — Part 3
Soprano Sax — Part 4

That one ‘band’ could easily be linked with a dozen different Songs and/or Patterns... just like a band can have many different compositions in their repertoire.

When in the MODX Performance Recorder you can *link* (blue interlocking chainlink icon) the Song (MIDI) or Pattern with any Performance... so that when you recall that musical composition, the instruments (the band), you used to create it will automatically be recalled.