poke ball (basic)
The most common variety of the Poké Ball.
In the anime and apparently most fanart, it has a simple red/white design.
In the games, it has the same design, but is often orange/white instead.
Naturally, it may be found in monochrome posts too. (Danbooru post #2661363)
Compare the tag Poké Ball, which encompasses all varieties of the Poké Ball, including Master Balls, Cherish Balls, Quick Balls, etc.
See also
This tag implicates poke_ball (learn more).