Every frame written sequentially in full lines — no interlaced fields, no flicker. Standard for cinema (24p) and modern digital acquisition.
Progressive scan means you record each frame completely in a single pass—line by line, from top to bottom, without delay or interludes. This is fundamentally different from interlacing, where two interleaved fields (odd and even lines) are written with a time delay to simulate flicker-free television. With progressive, all your image information is immediately present.
In cinema and modern digital workflows, we work almost exclusively progressively—24p for cinema, 25p for European standards, 50p for high-frame-rate production. This has massive advantages: you don't get combing artifacts with fast motion, object tracking in editing becomes cleaner, and slow-motion conversions work more losslessly. Especially with rotoscoping or when working with action, progressive immediately looks cleaner. Working with interlaced material is a punishment—the artifacts will bite you later in the edit.
Practically, this means: if your camera records in 1080i (like some broadcast cameras), you must deinterlace immediately or manually separate the fields. This always costs information. A better solution: choose 1080p or 720p progressive from the start. For archiving—especially with digital cinema DCP—progressive is the only standard. 4K material is expected to be progressive, period. If you need to convert legacy interlaced archives, you'll need a proper deinterlacer, otherwise your image will fall apart.
A pitfall: PAL television runs at 50i (interlaced), NTSC at 60i. If you have to deliver for TV broadcast in these formats, you first need to re-interlace from progressive—but this is automated and reversible. The actual creative material should always be progressive. For grading and VFX, progressive is non-negotiable. Modern camera sensor designs (RED, ARRI, Sony) always give you progressive raw images—that's the standard.