On Board Diagnostics

1 means 1st generation..

2nd generation became forced to standard in 1996. So ALL cars 1996 and newer have OBDII, some have OBDIII and other flavors... but 96 and newer has to have at least OBDII.

It's mainly the type of ECU. 95 and newer can have I. There are some benefits of using I vs II... and vice versa.