User-friendliness

User-friendly is a term often used to describe software and other technologies. Its definition is subjective, depending on the user. Useful alternative terms are usability and accessibility, both from the field of human-computer interaction.

Certain parameters can be used to judge it include

adequacy:: Only necessary input should be required.
learnability:: Manuals and instructions should be clear.
robustness:: Impact of error should be inversely proportional to probability of error.