I would call the main note an apex rather than a target note, because the term target note typically means any note that is approached or targeted. A melody could potentially have multiple target notes, whereas it probably only has 1-2 apexes. It sounds like you're asking about the main apex of a melody rather than a target note, partly because the B♭ (played over "sad") could qualify as a target note, while only the high F could be considered an apex. You're not asking about the B♭, which is a target note--you're asking about the F, which is an apex.
I'm getting the term apex from this page. This same page also has a good answer to your second question, "what is the significance of these lead-in notes?" Here's the brief answer: these lead-in notes form a crucial part of the contour of the melody. The contour can take any number of shapes, including an arch, an inverted arch, and a ramp. Here's how the site described this:
A good melody will have only 1 apex. This is the most important part of the phrase, so it should be set apart in its singularity.
Ways to highlight your apex might be to set it off by a leap [emphasis added] or placing it in an unexpected place (not beat 1 or 3 of a measure). Some possible contours include:
- An arch. Imagine an arch where the highest point is slightly to the right. A great place to put your apex is about 2/3 of the way into the melody as in the Traumerei of Schumann:
- An inverted arch. Imagine an upside down march. Sometimes it is effective to make your “apex” the lowest note of the melody. Beethoven does this brilliantly in Ode to Joy.
- A ramp. The apex of your melody will be at the beginning or the end in this contour. Somewhere Over the Rainbow is an excellent example of this contour. The composer’s highest note is at the beginning of the melody and the rest of the melody is spent descending to the low tonic.
So one way to describe these lead-in notes would be in terms of the contour/shape (e.g., the front of the arch, etc.). Beyond this, the lead-in notes are simply part of the melody.