just about is an adverb meaning "(of quantities) imprecise but fairly close to correct". It carries one recorded sense.
(of quantities) imprecise but fairly close to correct
“lasted approximately an hour”
“in just about a minute”
“he's about 30 years old”
“I've had about all I can stand”
“we meet about once a month”
“some forty people came”
“weighs around a hundred pounds”
“roughly $3,000”
“holds 3 gallons, more or less”
“20 or so people were at the party”
Definitions, synonyms and semantic relations for just about come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.