Absent additional context/hoping we're talking about the same 'Big 7': does this help answer your question?

In 1981, the US Army Intelligence and Threat Analysis Center produced this informational poster, titled 'The Soviet Big 7', illustrating seven armoured vehicles/weapons systems that then formed the backbone of the Soviet military:

• ZSU-23-4, a self-propelled anti-aircraft gun
• Mi-24, a helicopter gunship
• BMP, an armoured personnel carrier
• T-72, a main battle tank
• 2S1, a self-propelled 122mm howitzer
• 9K33, a vehicle-mounted surface-to-air missile launcher
• 2S3, a self-propelled 152mm howitzer

At the time, these were the primary combat vehicles that NATO forces were likely to encounter in the event of a military confrontation with the USSR. The poster was a training aid, designed to educate US Army personnel about the basic characteristics and capabilities of these vehicles, and to help them identify them by sight.