I just got back from a yoga class, The former director of the center is visiting so she gave a super advanced class with heavy pranayama and very long asana holds. Other than in private practice I am rarely able to effectively do japa in the headstand mudra as well as other asanas. It is very meditative to do so while in asana so detaching and peaceful as opposed to desiring of some outcome or release.
Beth japa is specifically referred to as repetition of the Lord's name and generally repetition of any mantra. I suppose the most famous being the Maha mantra:
Hare Rama Hare Rama - Rama Rama Hare Hare, Hare Krishna Hare Krishna, Krishna Krishna - Hare Hare.
japa can be part of meditation as well as your daily life. However it is meant to be dropped at some point so that you can meditate on No_thing.
My youngest asked and was deemed qualified to receive guru mantra from Sri Mata Amritanandamayi recently so he does japa and he immediately feels the divine presence of Mother and says that it relaxes him quicker than anything if he is anxious or upset.
My own mantra is an aspect of the Divine Mother also as she is inseperably connected to the male aspect.
So you have nama and rupa or name and object which for now are inseparable when you say the name of the Lord you automatically create your image of him which helps narrow and concentrate your focus.
There is sakti/power in every name of the Lord so choose whichever resonates with your being.
My name Ayeh-Asher-Ayeh is actually a form of divine name of the Lord.
When you perform Japa you mentally form and then conform to the qualities of that aspect of the Lord, for example the compassion of Yeshu/Issa/Jesus Siva or Yah, Krishna or Rama etc...you may use a mala or beads eventually japa goes from being conscious action to always being there. I hear the name of the Lord most anytime when I listen within.