A short section of music with a clear start and end quality, with a consistent or complementary musical character. Generally, the character is different from what comes after or precedes it, anywhere from subtly to very obvious.
Phrases happen over a specific number of s, usually 8 in tango, and frequently those have two smaller sections of 4 bars each, and those often divide further into two 2 bar segments. All very symmetrical; tango music usually is.
There is often a call and response or question and answer quality to the phrases and sub-phrases. Very often the 4 bar phrase is the dominant one with a distinct Q&A feeling.
(A note about the phrase in terms of the “count”. Dancers often misuse the word – at least in terms of how “beat” is defined by musicians. Whether there are 2 or 4 beats, as defined by the , tango dancers usually dance to 2 primary beats: beats 1 and 2 when the music is in “two”, and beats 1 and 3 when the music is in “four”. “Counts” rather than “beats” is a more accurate term to use in this case. Dancers add “counts”, at 2 per bar, so a 4 bar tango phrase has 8 counts. That’s why the so called “Eight Count Basic” step sequence is eight counts.)
See Phrasing for more details.
A bar or measure is a small segment of music containing all the number of beats as specified by the time signature.
Beat is the underlying and regularly spaced pulse of the music, measured in beats per minute. There are a fixed number of beats in a bar, indicated by the time signature. Tango (2/4, 4/8, 4/4) has 2 or 4 beats per bar, vals (3/4) has 3 and milonga (2/4) has 2.
(There may be a sense of 4 beats even though the time signature is 2/4. Tango very often subdivides the 2/4 beat, doubling the count from 2 to 4, effectively using a 4/8 time signature. Some tango music is explicitly written in 4/8, most are in 2/4. See Tango Time Signatures and the Beat).
The two numbers, one above the other, written near the beginning of the first staff line (or whenever it changes), specifying the number of beats in a measure and the type of note that gets one beat.