In "The Cage" and "Menagerie" Pike specifically tells the crew "Time Warp Factor" instead of "warp factor". Possibly it was shortened to plain warp factor by the series.
In "The Cage" and "Menagerie" Lt. Tyler also says that the "time barrier" his been broken and new ships are faster. Thus it would seem that the "space warp" discovered by Cochrane ("Metamorphosis") was used in the original warp drive but newer warp drive also has a "time Warp".
In "Where No Man Has Gone Before" the "space Warp" was disabled but it seems certain that the Enterprise was still able to use the "time warp" generators to either ONE) travel several light days at faster than light speeds or to TWO) travel several light days at slower than light speeds but slow down the passage of time aboard so that less than a single day passed aboard, or THREE) possibly both.
This "time warp" ability explains how doing something new and different with the engines sent the Enterprise back in time in "The Naked Time".
If the "space warp" in warp drive is similar to the theoretical Alcubierre Warp Drive it would warp space around the ship and created a warped bubble of space time to propel the ship faster than light as seen from outside the warp bubble.
The "time warp" which was introduced about 13 to 31 years before the first season of TOS may have been used in conjunction with the "space warp" to either one) make interstellar travel seem faster to outside observers, or two) make interstellar travel seem faster to the crew aboard the ship or three) do both.
When the Enterprise's "space warp" capability was disabled in "Where no Man has gone before" the speed of the Enterprise was dropped to just a few percents - or even less - of its previous speed.
Bu the Enterprise was still apparently able to use its "time warp" capability along with the impulse engines to travel a distance of several light days while only a few hours pass on the ship (and possibly also in the outside universe). The alternative is to imagine that the Enterprise's impulse engines could achieve faster than light speeds.
Nobody seems to believe that the TOS Enterprise had a faster-than-light impulse drive or that it could warp time with its engines, but the dialog in "Where No Man Has Gone before" seems to prove that one or the other, or possibly both, is correct.
If, as some people think, different generations of warp drive were described as "space warp", "time warp", "transwarp" etc., it is possible that an early form of warp drive was called "impulse warp drive" for some technical reason, and by Kirk's era "impulse warp drive" was sometimes called "impulse drive" (confusing it with the current impulse drive) and sometimes called "warp drive".
Or it is possible that impulse drive was always totally different from warp drive and that at one time impulse drive was a rival and alternate form of faster-than-light drive but by Kirk's era warp drive was clearly superior for faster-than-light travel and impulse drive was only used for slower-than-light travel and the impulse engines used were no longer designed to go faster than light.
David Winfrrey in "Falling Out of Standard Orbit" in The Best of Trek # 16, 1991, is one of several writers who have pointed out contradictions between common theories of treknology and the evidence of the episodes. Winfrey cites events in several episodes and movies to claim that impulse drive must still be capable of hyperlight speeds even during the eras of Kirk and Picard.
He ends with a quote from The Next Generation episode "Conspiracy":
Riker: "Increase to warp six."
LaForge: "Aye, sir. Full Impulse."
If LaForge made a mistake, maybe he meant to say "full warp". But full warp for the Enterprise D is over warp factor nine in the new scale so he couldn't go to full warp to reach warp six.
Perhaps the various warp factors of the Enterprise D were combinations of space warp and time warp and LaForge increased either the space warp or the time warp to full strength in order to reach warp six and so meant to say either "full space warp" or "full time warp" when he said "Full impulse".
Or perhaps the Enterprise D uses combinations of warp drive and impulse drive to reach various warp factors and LaForge increased the impulse drive to full power to achieve warp factor six. Then LaForge was correct to say "Full impulse" and the next generation Technical Manuel is incorrect about how the Enterprise D functions.