EAL in IT is a numerical evaluation of an IT product or system according to the Common Criteria security evaluation, an international standard valid from year 1999. In the standard, there are 7 levels - EAL1 to EAL7. The higher the number, the higher the assurance requirements, which an evaluated target must fulfill to obtain a Common Criteria certificate.
The EAL doesn’t directly translate to the level of security of said target, it only evaluates how well the system is tested to be secure. The higher the EAL, the more expensive it is.