What is Six Acts?

Legal Definition
In Britain, following the Peterloo Massacre of August 16, 1819, the British government acted to prevent any future disturbances by the introduction of new legislation, the so-called Six Acts aimed at suppressing any meetings for the purpose of radical reform.

Élie Halévy considered them a panic-stricken extension of “the counter-revolutionary terror...under the direct patronage of Lord Sidmouth and his colleagues” ; later historians have tended to see them as relatively mild gestures towards law and order, only tentatively enforced.
-- Wikipedia
Legal Definition
The acts passed in 1819, for the pacification of England, are so called. They, in effect prohibited the training of persons to arms; authorized general searches and seizure of arms; prohibited meetings of more than fifty persons for the discussion of public grievances; repressed with heavy penalties and confiscations seditious and blasphemous libels; and checked pamphleteering by extending the newspaper stamp duty to political pamphlets. Brown.