Birth spacing has emerged since the early 1980s as a key concept to improve maternal and child health, triggering interest in birth spacing practices in low-income countries, and drawing attention to prevailing norms in favour of long birth intervals in West Africa. In Senegal, the Wolof concept of Nef, which means having children too closely spaced in time, is morally condemned and connotes a resulting series of negative implications for family well-being. While Nef and "birth spacing" intersect in key ways, including acknowledging the health benefits of longer birth intervals, they are not translations of each other, for each is embedded in distinct broader cultural and political assumptions about social relations. Most notably, proponents of the demographic concept of birth spacing assume that the practice of using contraception after childbearing to postpone births could contribute to "empowering" women socially. In Senegal, by contrast, preventing Nef (or short birth intervals) is also viewed as strengthening family well-being by allowing women to care more fully for their family. This paper draws on policy documents and interviews to explore women's and men's understanding of Nef, and in turn critically reflect on the demographic concept of birth spacing. Our findings reinforce the relevance of the concept of birth spacing to engage with women and men around family planning services in Senegal. Accounts of the Nef taboo in Senegal also show that social norms stigmatising short birth intervals can legitimise constraints faced by women on control of their body.