Could any one explain the difference
This question appears to be off-topic. The users who voted to close gave this specific reason:
- "Basic financial questions are off-topic as they are assumed to be common knowledge for those studying or working in the field of quantitative finance." – pyCthon, olaker
What Tick data you have in mind? NASDAQ ITCH is tick data but you have to construct the limit order book yourself to keep track of the best bid and ask price for each stocks. Not a trivial task. If you get TAQ data, you will get the best bid and ask (NBBO) but TAQ data has some issues like no odd-lot trades and trades are not mark buyer or seller initiated.