While doing meditation I had experienced sudden stop of mind for a second. Then restart again reflecting that is peaceful. What was that experienced?is it stream entry?
Stream Entry (Sotāpanna) is a particular state in which someone practicing the dharma has broken the first three fetters (impediments to advancement). These are:
- The fetter of self-view: the belief that there is an I/me (a self) that is eternal and unchanging, or by contrast the rejection of such a belief. One comes to realize it is an unimportant question that causes headaches.
- The fetter of rites and rituals: the belief that one can reach liberation merely through the observance of rites, rituals, ethical strictures, or other 'formal' practices. One comes to realize that one must engage the dharma more deeply through meditation.
- The fetter of doubt: an intellectual understanding of the dharma that is subject to question, which is replaced by an experience of the fruits of practice that is beyond doubt.
The cessation of mental activity for a brief moment may or may not be sufficient to break the third fetter; only you can say whether you still have doubts. It is a useful and interesting experience in any case, one which demonstrates that your practice is sound. But don't worry (or think) too much about it. An undue focus on the meaning or significance of events can lead you back into the second fetter, where you ritualize the appearance of certain states as symbols of progress.