The phrase "large segment" refers to a big or significant part of something. It describes a portion or group that is sizeable or substantial compared to the whole. Full definition
Overall, we find that the market comprises a combination of large segments of similar schools and smaller segments of like institutions, but also some schools that are truly unique. (educationnext.org)
This lack of geographical mobility for large segments of the population undermines the competitive pressure that low - performing schools and school districts would otherwise expect to face. (educationnext.org)
In more practical terms, it would be regarded as a scandal by large segments of the press and public, who hold the Queen in much higher esteem than elected politicians. (politics.stackexchange.com)