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What are the factors in the Drake equation?

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Planet TOI 700e — extraterrestrial life An illustration of the Earth-size planet TOI 700e orbiting within the habitable zone of its star. The habitable zone is the area around a star where liquid water, and thus possibly life, can survive on a planet's surface. Its Earth-size sibling, TOI 700d, can be seen in the distance.

The Drake equation is a mathematical formula used to estimate the number (N) of active, communicative extraterrestrial civilizations in the Milky Way Galaxy. It is expressed as:

N = RfpneflfifcL*

The factors are defined as follows:

R_*: The mean rate of star formation in the galaxy.
f_p: The fraction of those stars that possess planetary systems.
n_e: The average number of planets per system that are ecologically suitable for life.
f_l: The fraction of those suitable planets on which life actually emerges.
f_i: The fraction of life-bearing planets where intelligent life evolves.
f_c: The fraction of civilizations that develop technology capable of interstellar communication.
L: The average length of time such civilizations continue to broadcast these signals into space.12

Because these variables are difficult to quantify, the equation serves primarily as a framework for discussing the search for extraterrestrial intelligence rather than providing a definitive count.1