General Definition:
1. A small hand-held device which is operated by pushing buttons, or any thing or any action directly or indirectly associated with this, especially a calculator or mobile phone.
As a Noun:
1. A small electronic device that you use for doing mathematical calculations. English = calculator.
2. A small portable telecommunications device that you use for making phone calls. You dial the number by pushing on buttons. English = mobile phone.
As a Verb or Adjective:
1. To use a small hand-held device, such as a calculator or portable phone, by pushing its display buttons.