A Military Operations Area (MOA) depicted on a sectional chart indicates:
Why →MOAs separate certain military training from IFR traffic and advise VFR pilots of potential hazards. Unlike Restricted Areas, no clearance is required to enter a MOA. However, pilots should exercise extreme caution when the MOA is active. ATC can advise on current activity level.
The trap →MOAs don't prohibit entry for non-military aircraft. That's the difference from Restricted and Prohibited Areas. "Can enter without clearance" doesn't mean safe when active. High-speed military aircraft at low altitude in an active MOA present a genuine collision risk.
Field note →For drone ops near MOAs, call the controlling agency (listed in the Chart Supplement) or ask ATC whether it's active. Military training jets can exceed 400 knots at low altitude with virtually no warning time.