There's ac current gain, particularly high frequency value "hfe". Then there's low frequency/dc value "hFE".
hFE = Ic/Ib.
hfe = ic/ib.
"Ic, Ib" are the dc current values, & "ic, ib" are the sc current values.
As frequency increases, more base current, ac part, is needed for a specific value of ac collector current. Eventually, at some particular value of frequency, ic/ib = hfe takes a value of unity. This frequency is called the "transition frequency", aka "ft".