In simple words Form 16 is a statement given by employer to employee providing details of Salary credit and TDS deduction for the period of Employment. There can be more than one Form 16 for an individual for the FY.
Whereas 26AS is a TDS credit statement. It may contain TDS not only from salary u/s 192B but also contains TDS under various other Sections, Advance tax paid, Interest on Tax refund etc..