SysEx = System Exclusive It's information transmitted over midi for one specific end device. Generally, it's used to dump patches to/from a synth. Or, for dumping a firmware upgrade to a synth.
SysEx is really useful for specific applications. But, it's a pain in the ass a lot of the time.

General MIDI (GM) is a defined standard set of 128 Patches adopted to make sound modules more compatible. The 128 Patches appear in a specific order.
As examples, Patch number 1 on all GM sound modules is always the sound of an Acoustic Grand Piano and Patch number 25 is always a Nylon String Guitar. In this way, no matter what MIDI sound module you use, when you change to a specific Patch number, you always hear the same type of sound. The chart, GM Patches, shows you the names of all GM Patches, and their respective Program Change numbers.
The patches are arranged into 16 "families" of instruments, with each family containing 8 instruments. For example, there is a Reed family. Among the 8 instruments within the Reed family, you will find Saxophone, Oboe, and Clarinet.
A GM sound module should be multi-timbral, meaning that it can play MIDI events upon all 16 channels simultaneously, with a different GM Patch sounding for each channel. This always you to orchestrate and layer GM sounds.
GM also has a "drum module" allowing each Drum Part to trigger MIDI a different drum sound. The assignment of GM drum sounds to MIDI notes is shown in the chart, GM Drum Sounds. The Drum Part is usually automatically set to receive MIDI data on channel 10.
GM makes it easy for musicians to put Program Change messages in MIDI sequencer song files. The messages select the correct instruments on all GM sound modules and play all of the correct instrumentation automatically.
GM also spells out other minimum requirements that a GM module should meet, such as being able to respond to Pitch and Modulation Wheels and to play notes simultaneously with dynamics among the 16 Parts. These standards ensure that MIDI Files play back properly on various types of sound modules, keyboards and drum machines.
MIDI specifications are not limited to the GM standard. Patches can be set up to play entirely different sounds than the GM set and most MIDI sound modules and keyboards offer such programmability, with hundreds, if not thousands, of different sounds. Almost all have a GM option to allow an easy interface.
NOTE: GM does not control the quality of the sound produced. For example, one sound module could use FM synthesis to simulate the Acoustic Grand Piano patch, while another may use 24 bit digital audio waveforms of sampled piano sounds.

General MIDI Level 1 Instrument Families
The General MIDI Level 1 instrument sounds are grouped by families. In each family are 8 specific instruments.
PC#	Family Name
1-8	Piano
9-16	Chromatic Percussion
17-24	Organ
25-32	Guitar
33-40	Bass
41-48	Strings
49-56	Ensemble
57-64	Brass
65-72	Reed
73-80	Pipe
81-88	Synth Lead
89-96	Synth Pad
97-104	Synth Effects
105-112	Ethnic
113-120	Percussive
121-128	Sound Effects

General MIDI Level 1 Instrument Patch Map
Note: While GM1 does not define the actual characteristics of any sounds, the names in parentheses after each of the synth leads, pads, and sound effects are, in particular, intended only as guides).
PC#	Instrument Name
1.	Acoustic Grand Piano
2.	Bright Acoustic Piano
3.	Electric Grand Piano
4.	Honky-tonk Piano
5.	Electric Piano 1
6.	Electric Piano 2
7.	Harpsichord
8.	Clavi
9.	Celesta
10.	Glockenspiel
11.	Music Box
12.	Vibraphone
13.	Marimba
14.	Xylophone
15.	Tubular Bells
16.	Dulcimer
17.	Drawbar Organ
18.	Percussive Organ
19.	Rock Organ
20.	Church Organ
21.	Reed Organ
22.	Accordion
23.	Harmonica
24.	Tango Accordion
25.	Acoustic Guitar (nylon)
26.	Acoustic Guitar (steel)
27.	Electric Guitar (jazz)
28.	Electric Guitar (clean)
29.	Electric Guitar (muted)
30.	Overdriven Guitar
31.	Distortion Guitar
32.	Guitar harmonics
33.	Acoustic Bass
34.	Electric Bass (finger)
35.	Electric Bass (pick)
36.	Fretless Bass
37.	Slap Bass 1
38.	Slap Bass 2
39.	Synth Bass 1
40.	Synth Bass 2
41.	Violin
42.	Viola
43.	Cello
44.	Contrabass
45.	Tremolo Strings
46.	Pizzicato Strings
47.	Orchestral Harp
48.	Timpani
49.	String Ensemble 1
50.	String Ensemble 2
51.	SynthStrings 1
52.	SynthStrings 2
53.	Choir Aahs
54.	Voice Oohs
55.	Synth Voice
56.	Orchestra Hit
57.	Trumpet
58.	Trombone
59.	Tuba
60.	Muted Trumpet
61.	French Horn
62.	Brass Section
63.	SynthBrass 1
64.	SynthBrass 2
65.	Soprano Sax
66.	Alto Sax
67.	Tenor Sax
68.	Baritone Sax
69.	Oboe
70.	English Horn
71.	Bassoon
72.	Clarinet
73.	Piccolo
74.	Flute
75.	Recorder
76.	Pan Flute
77.	Blown Bottle
78.	Shakuhachi
79.	Whistle
80.	Ocarina
81.	Lead 1 (square)
82.	Lead 2 (sawtooth)
83.	Lead 3 (calliope)
84.	Lead 4 (chiff)
85.	Lead 5 (charang)
86.	Lead 6 (voice)
87.	Lead 7 (fifths)
88.	Lead 8 (bass + lead)
89.	Pad 1 (new age)
90.	Pad 2 (warm)
91.	Pad 3 (polysynth)
92.	Pad 4 (choir)
93.	Pad 5 (bowed)
94.	Pad 6 (metallic)
95.	Pad 7 (halo)
96.	Pad 8 (sweep)
97.	FX 1 (rain)
98.	FX 2 (soundtrack)
99.	FX 3 (crystal)
100.	FX 4 (atmosphere)
101.	FX 5 (brightness)
102.	FX 6 (goblins)
103.	FX 7 (echoes)
104.	FX 8 (sci-fi)
105.	Sitar
106.	Banjo
107.	Shamisen
108.	Koto
109.	Kalimba
110.	Bag pipe
111.	Fiddle
112.	Shanai
113.	Tinkle Bell
114.	Agogo
115.	Steel Drums
116.	Woodblock
117.	Taiko Drum
118.	Melodic Tom
119.	Synth Drum
120.	Reverse Cymbal
121.	Guitar Fret Noise
122.	Breath Noise
123.	Seashore
124.	Bird Tweet
125.	Telephone Ring
126.	Helicopter
127.	Applause
128.	Gunshot