Runtime can be synonymous with execution time, referring to the duration in which a program or process is in operation. It can also be known as processing time, indicating the period during which a computer performs tasks or calculations. Another synonym for runtime is operating time, encompassing the interval in which a device, system, or software is functioning. Additionally, the term can be interchanged with active time, suggesting the duration in which a program is actively running and producing desired outputs. Overall, these synonyms capture the essence of the word "runtime" and can be utilized to convey similar concepts within computer science and technology discussions.