I've studied direct modulation and I understood it.
I've tried searching about "melodic modulation", but I couldn't find the meaning of it.
Could you please explain to me what "melodic modulation" is in music?
That’s what I’ve found about Modulation in the melody
In many folk songs or chorales, modulation is already predetermined by the melody.
and the this example:
It shows how the melody is “modulating” from D to A-major and B-minor using melodic segments and leading tones(by augmentation = sharp -> lead-tone).
Wiki e says:
Melodic: recognizable segment of the scale of the quasi-tonic or strategically placed leading-tone
'Direct modulation' is a widely-used term for when you reach a cadence in one key then directly set off in a different one. No pivot chord or modulatory passage.
As you have discovered from your lack of search results, 'Melodic modulation' is not a standard term. So its definition is whatever you want it to be! (Where did you encounter the term? If in a textbook, THAT'S where you should look for the writer's definition of what he means by it.)
What MIGHT 'Melodic modulation' mean? Well, obviously there's going to BE a melody, not just a chord sequence. If you're playing in C major and start introducing F sharps, the melody could be said to be taking us on a melodic modulation into G major. (Presumably the chords will follow. Which might explain why describing 'Melodic modulation' as a separate thing doesn't happen much.)