NS44 jee is correct. As fas as we are concerned, they all mean doing Gurmat Naam Abhyaas.
If you want to become more specific, Jaap is related to Chanting Naam employing Rasna or Hirda. Of course, Dhyaan has to be there. Bhai Sahib Randhir Singh jee has written that Jaap employs either Rasna or Hirda or both but Simran can be done in pure Surti.
The meaning of the word Simran is to remember i.e. Yaad Karna. So it can be done in Surti as well. Doing something in pure Surti means not employing the body at all and doing Naam Abhyaas or Gurbani Paath in Surti alone.
In any case, the above is becoming too technical. The aim is to do Naam Abhyaas and Gurbani Paath. Whether it's done in Surti or Rasna, or Hirda, depends entirely on how one prefers to do at a given time. There is nothing but Laaha in doing Naam Abhyaas and Gurbani Paath.
Kulbir Singh