E stands for Evolution (or Entwicklung in German), and stands for a
code for each type of BMW.
Here is a fuller list of codes:
ps In the future BMW is out of E-numbers, and will go on in F-numbers
These are the chassis designations. E36 is the 3 Series chassis from 1993
until 1999, then the 3 Series became the E46 until either 2006 or 2007
models, then it became the E90.
The sedan and coupe generally do not change chassis design in the same year,
therefore the 4 door became the E46 a year after the coupe (but this is a
level of detail that you didn't ask about, and it confuses the matter
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