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"La cantante" is a form of "cantante", a noun which is often translated as "singer". "El" is a form of "el", a definite article which is often translated as "the". Learn more about the difference between "la cantante" and "el" below.
el cantante, la cantante(
kahn
-
tahn
-
teh
)This means that the noun can be masculine or feminine, depending on the gender of the noun it refers to (e.g., el doctor, la doctora).
a. singer 
De día es abogada, pero de noche es la cantante principal en una banda.By day she's a lawyer, but at night she's the lead singer in a band.
el(
ehl
)A definite article is a word that identifies a noun as specific or known to the speaker (e.g., the girl).