Ive always been taught
and it looks like the link faceless provided says the same thing
To set things straight. Planometric view is a view where all vanishing points are infinite, meaning that all lines that are parallel will appear parallel on paper too. Most planometric drawings place the vertical ribs orthogonal to the surface, meaning they are 90° with the "under side of the paper". The other two directions tend to be 0, 30, 45 or 60 degrees. There's for example the 0°,45° called cavalier perspective (the one featured in most nes games, look in the background contest for examples). You've got perspectives with 30°,60° and 60°,30° like shown in Takam's example.
Another planometric perspective is the isometric perspective which is a perspective where one direction is orthogonal (straight lines up) and the other two equal, but mirrored, so this means that 30°,30° is isometric. The middle of the three planometric examples Takam gave is isometric too however, as it's 45°,45°.
All isometric views are also planometric, and so alot of so-called planometrics are also isometric. Isometric isn't always 30°,30°, it can be anything, and so the pixelart isometric view (26,...° or whatever) is a valid isometric perspective, and not a slightly altered bastardized perspective like some say...
