SQL Server tables: what is the difference between @, # and ##?

#table refers to a local (visible to only the user who created it) temporary table.

##table refers to a global (visible to all users) temporary table.

@variableName refers to a variable which can hold values depending on its type.

Have a look at

• Temporary Tables vs. Table Variables and Their Effect on SQL Server Performance
• Differences between SQL Server temporary tables and table variables
• Temp Tables and Table Variables: When To Use What And Why