BACKGROUND: Frailty is a suggested consequence of ageing, but with a variety of different definitions the understanding of what it means to be frail is challenging. There is a common belief that frailty results in a reduction of physical functioning and ability and therefore is likely to significantly affect a person's quality of life. The aim of this study was to explore the understanding of older people about the meaning of frailty and the potential consequences of being classified as frail. METHODS: This paper forms a secondary analysis of a process evaluation of a complex intervention that was embedded within the individually randomised Home-based Extended Rehabilitation of Older people (HERO) trial. A maximum variation, purposive sampling strategy sought to recruit participants with a wide range of characteristics. Data collection included observations of the delivery of the intervention, documentary analysis and semi-structured interviews with participants. Thematic analysis was used to make sense of the observational and interview data, adopting both inductive and deductive approaches. RESULTS: Ninety three HERO trial participants were sampled for the process evaluation with a total of 60 observational home visits and 35 interviews were undertaken. There was a wide range in perceptions about what it meant to be classified as frail with no clear understanding from our participants. However, there was a negative attitude towards frailty with it being considered something that needed to be avoided where possible. Frailty was seen as part of a negative decline that people struggled to associate with. There was discussion about frailty being temporary and that it could be reduced or avoided with sufficient physical exercise and activity. CONCLUSION: Our study provides insight into how older people perceive and understand the concept of frailty. Frailty is a concept that is difficult for patients to understand, with most associating the term with an extreme degree of physical and cognitive decline. Having a label of being "frail" was deemed to be negative and something to be avoided, suggesting the term needs to be used cautiously. TRIAL REGISTRATION: ISRCTN 13927531. Registered on April 19, 2017.