Classic temperament is a measurement of "Expressiveness" and "responsiveness". Expressiveness is how much we are inclined to approach others for interaction, and responsiveness is how much we want or allow others to approach us (according to certain criteria).
Anciently, this was recognized in terms of the temperature and texture of four body fluids assumed to cause the temperament behaviors. "Hot" or "warm" is expressive, "cold" is reserved, "moist" is responsive, and "dry" is reluctant or resistant.
When they realized the four body "humours" didn't cause the behaviors, and that it was likely apart of personality, expressiveness came to be termed as long or short "response time delay" (basically, how quick you are to react toward others), while responsiveness was "response time sustain" (how long you held on to these reactions).
Eventually, expressiveness became introversion and extroversion (later realized to be connected with how over- or under- stimulateable you are to the environment), and responsiveness became "people" vs "task" focus.
This often manifests through outward behavior, but it's about the "underlying
needs" of the temperaments driving those behaviors (which could be masked by other behaviors for various reasons, and that's why you can't always go by behavior).
In the type system, Keirsey first tried to map the four temperaments to the types, but he filtered them through other systems such as Kretschmer's character styles. This version was ultimately derived from Plato's "four types of men", which are the final names he used, rather than the Hippocrates/Galen "humour"-based ones. So rather than using expressiveness and responsiveness, he found they mapped to MBTI's S/N, and another dimension (derived from another factor he derived from someone else), which he called "Cooperative/Pragmatic".
His temperaments however, were totally "blind" to the original temperament factor of I/E. (Each temperament consists evenly of two I's and two E's. Meanwhile, S/N actually tied together what corresponded to opposite temperaments like Sanguine and Melancholy; e.g. the SP and SJ). What he had not realized right away, were that there are TWO levels of temperament in type. A "social" level, and a "taking action" level, called "conative". His temperaments were actually the conative ones. So Linda Berens discovered where the social temperaments fit in type, and called them the "Interaction Styles" (which Keirsey actually later adopted under the generic "roles of interaction" in his two last books). These now are based on I/E, and people/task (renamed "informing"/"directing"), which tie, in a sort of alternating fashion, to both T/F and J/P. On the conative level, Keirsey's "cooperative/pragmatic" would actually be the "expressiveness" of that area, while another informal dimension he called "contagious" vs" annoying", and by Berens, "motive" vs "structure", would be responsiveness.
http://www.erictb.info/temperament1s.html