Jelqing is a manual exercise that's been part of PE communities for decades. The basic technique: using a partial erection (50-75%), grip the base with the OK grip, and slowly milk the hand toward the glans, stopping before the glans. The theory is that this forces blood into the erectile tissue under pressure, and over time this repeated engorgement causes the erectile chambers to expand in capacity.
What the scientific evidence actually says: almost nothing — there are virtually no peer-reviewed studies on jelqing. The evidence base is almost entirely anecdotal, from PE communities where selection bias is enormous (people who got results post, people who didn't often leave).
What the honest PE community generally agrees on: temporary engorgement from a session is real. Permanent gains from months of jelqing are reported by some but are modest at best — typically small girth increases reported after 6-12 months of consistency. Many men report no permanent change at all.
— JelqJourney_Marcus