Web-DL stands for Web Download. This means the video file was ripped directly from a streaming service (like Hoichoi, Zee5, or Amazon Prime Video) without re-encoding from a broadcast or disc source. Web-DLs are usually superior in quality to HDTV or DVD rips because they come from the original compressed stream.
Likely a misspelling or compressed form of Prem Amar. Such abbreviations are common in scene releases to save characters. premamar20091080pwebdlbengalix264skymov
The audio language. In this case, Bengali. Often these releases include the original language track and sometimes dubbed versions. Web-DL stands for Web Download