Driven by the vast proliferation of mobile devices and ubiquitous computing, dynamic software adaptation is becoming one of the most common terms in Software Engineering and Computer Science in general. After the evolution in autonomic and ubiquitous computing, we will soon expect devices to understand our changing needs and react to them as transparently as possible. Software adaptation is not a new term though; it has been extensively researched in several domains and in numerous forms. This has resulted in several interpretations of adaptation. This survey aims to provide a disambiguation of the term, as it is understood in ubiquitous computing, and a critical evaluation of existing software adaptation approaches. In particular, we focus on existing solutions that enable dynamic software modifications that happen on resource constrained devices, deployed in mobile and ubiquitous computing environments.