What does Mercury Retrograde mean?
In mythology, Mercury is the messenger of the gods. Astrologically, the planet Mercury is said to be associated with or to rule all activities that relate to communications, travel, learning such as:

signing agreements
classes and schools
sending correspondence
communications equipment such as computers, radios, and phones
traveling and travel equipment such as cars, bicycles, trains, and planes
Classically, Mercury retrograde periods are not considered ideal
for engaging in Mercury related activities such as:
placing ads
making important decisions
travel
purchasing communications equipment
signing contracts
initiating business deals
sending important correspondence or any type of message
starting school or any important project
beginning any new enterprise (as plans may be reversed later)
A Mercury retrograde period is thought to be excellent for:
reviewing and revising plans
catching up on old business
cleaning out the metaphorical closet
deeply considering issues