Off all the confusing terms associated with Cuban music, "songo" may be the hardest to define. It's commonly used to describe:

1)  The music of Los Van Van ... all of it.

2)  The music of Cuba in the 70s and 80s ... most of it.

3) The most common Cuban genre of the 70s and 80s, as typified by Los Van Van, Ritmo Oriental, Irakere, Los Reyes 73, Grupo Monumental, etc. (in spite of the fact that many members of these groups adamantly insist that their music is not "songo").

4)  A specific rhythm with the following characteristics:

a)  A brisk tempo of 105-130 beats per minute (source) - slightly slower than most guaguancó (115-150 bpm) (source) but faster than most timba (90-105 bpm) (source), and much faster than Arsenio's son montunos (60-80 bpm) (source).

b) 2-3 rumba clave

c) The timbalero's kit is augmented or replaced by drumset elements, especially the bass drum.

note: a, b, and c were already present in Pello el Afrokán's mozambique (source) style of the early 60s.

d) Conga marchas based on a composite of the tumba and quinto drums of rumba guaguancó and often featuring melodic combinations of open tones. (source)

e) Bass tumbaos that begin on the downbeat of the measure, followed by a series of offbeats and clave-aligned accents, usually including the ponche of the 3-side. (As opposed to the bombo-ponche pattern - xxx0 xx0x xxx0 xx0x - dominant in the Nuyorican salsa of the same period.)

note: Both types of bass tumbao can be found in pre-songo, pre-salsa Cuban music, although from the beginning, Formell added his share of original permutations.

5) An eclectic mix of rhythmic and harmonic experiments by Formell and others that depart completely from the tendencies listed in definition #4, including slow, backbeat-heavy drumset rhythms (source) derived from rock and funk.

6)  A section of a timba arrangement where one or more of the rhythm section instruments plays a pattern derived from songo. For example, Paulito FG's 1998 group had a gear called songo con efectos in which the conga marcha was based on Changuito's bota rhythm (source). Klímax also frequently uses songo-flavored sections (source), and Pupy y Los Que Son Son's style (source), in general, is referred to as songo, although it's quite different from early Los Van Van.

One would be hard-pressed to find a better example than Cuban music to demonstrate the Gestalt principle that "the whole is greater than the sum of the parts". We have Arsenio and Lilí, Paulito and Ceruto, Manolín and Luis Bu, Calzado and JC González, Calzado and Tirso Duarte ... the list goes on and on, but the most famous and longest-running creative collaboration was the trio of Juan Formell, César "Pupy" Pedroso, and, last but not least, José Luis Quintana, better known simply as "Changuito".