Calendarific is an online API service that provides comprehensive access to a wide array of global holidays and observances. It allows developers to easily integrate holiday and observance data into their applications with coverage for more than 230 countries and regions, along with detailed information on public holidays, religious occasions, and other significant events. The platform is designed to support various use cases, such as planning applications, content creation, or market analysis. Users can access the API through a subscription model, which offers different tiers to cater to varying needs and usage levels.