English: femtocell 
Welsh: cell fechan
Subject: TGCh
Welsh definition: Small cells (“femtocells”) are miniature cellular base stations. They provide a low-power signal much closer to mobile users than traditional macro networks, which they complement, resulting in better voice quality, higher data performance and better battery life. The term femtocell was originally used to describe residential products, with picocell being used for enterprise/business premises and metrocell for public/outdoor spaces. As the underlying femtocell technology expanded to address this wider scope, the term small cell was adopted to cover all aspects. 
Plural: celloedd bychan