Convertible Note A convertible note is a vehicle for raising funding. It's a promissory note, but instead of being repaid as cash, the debt is converted into equity during your next priced round.
Valuation Cap - Uncapped The valuation cap puts a ceiling on the valuation at which the note converts to equity. If you raise at a $6mm valuation and an investor holds a note with a $3mm valuation cap, their equity is allocated as if the valuation were at $3mm.
Uncapped means that there is no valuation cap. The note will convert at the $6mm valuation.
MFN (Most Favored Nation) clause A most favored nation clause guarantees that investor the best terms - if you offer a second investor a better deal, the first investor gets upgraded to that deal as well.
All together: An uncapped convertible note with an MFN clause Putting it together, these notes are the most flexible terms you can possibly have.