There is a lack of knowledge and understanding of the term exclusive breastfeeding (EBF) among health professionals. The purpose of this review was to examine the best available literature on mothers' understanding of the term EBF. A systematic search of eight electronic databases (Medline, Embase, CINAHL, CDSR, CENTRAL, Cab Abstracts, Scopus and African Index Medicus) was conducted (Protocol registration in PROSPERO: CRD42015019402). All study designs were eligible for inclusion. Studies were included if they: (1) involved mothers aged 18 years or older; (2) assessed mothers' knowledge/understanding/awareness of the term 'EBF'; (3) used the 1991 WHO definition of EBF and (4) were published between 1988 and 2015. Two reviewers retrieved articles, assessed study quality and performed data extraction. Of the 1700 articles identified, 21 articles met the inclusion criteria. Quantitative findings were pooled to calculate a proportion rate of 70.9% of mothers who could correctly define EBF, although the range varied between 3.1 and 100%. Qualitative findings revealed three themes: (1) EBF was understood by mothers as not mixing two milks; (2) the term 'exclusive' in EBF was incorrectly understood as not giving breast milk and (3) mothers believing that water can be given while exclusively breastfeeding. Research investigating aspects of self-reported EBF may consequently be unreliable. A standardised tool to assess mothers' knowledge of EBF could provide more accurate data. Public health campaigns should emphasise EBF to target mothers, while addressing the education of health professionals to ensure that they do not provide conflicting advice.