What is Unlawful Assembly?

Legal Definition
Unlawful assembly is a legal term to describe a group of people with the mutual intent of deliberate disturbance of the peace. If the group are about to start the act of disturbance, it is termed a rout; if the disturbance is commenced, it is then termed a riot. In Britain, the offence was abolished in 1986.
-- Wikipedia
Legal Definition
Crim. law. A disturbance of the public peace by three or more persons who meet together with an intent mutually to assist each other in the execution of some unlawful enterprise of a private nature, with force and violence; if they move forward towards its execution, it is then a rout (q. v.) and if they actually execute their design, it amounts to a riot. (q. v.) 4 Bl. Com. 140; 1 Russ. on Cr. 254; Hawk. c. 65, s. 9; Com. Dig. Forcible Entry, D 10; Vin. Abr. Riots, &c., A.
-- Bouviers Law Dictionary
Legal Definition
At common law. The meeting together of three or more persons, to the disturbance of the public peace, and with the intention of co-operating in the forcible and violent execution of some unlawful private enterprise. If they take stej)s towards the performance of their purpose, it becomes a rout; and, if they put their design into acfual execution, it is a riot. 4 Bl. Comm. 146. Any meeting of great numbers of people, with such circumstances of terror as cannot but endanger the public peace, and raise fears and jealousies among the subjects of the realm. 4 Steph. Gomm. 254.
-- Black's Law Dictionary
Legal Definition
In criminal law. The assembling of three or more persons together to do an unlawful act, who separate without actually doing it, or making any motion towards it. 3 Inst. 176; 4 Bl. Comm. 146. It differs from a riot or rout, because in each of the latter cases there is some act done besides the simple meeting. See State v. Stalcup, 23 N. O. 30, 35 Am. Dec. 732 ; 9 Car. & P. 91, 431; 5 Car. & P. 154; 1 Bishi Crim. Law, § 535 ; 2 'Bish. Orim. Law, §§ 1256, 1259.
-- Black's Law Dictionary
Legal Definition
A disturbance of the peace by persons assembling together with an intent to do a thing which, if executed, would make them rioters, but neither executing it nor making any motion toward its execution. See 128 N. Y. 108, 26 Am. St. Rep. 458, 27 N. E. 970.
-- Ballentine's Law Dictionary