Microsoft has updated its servicing model. The Semi-Annual Channel is a twice-per-year feature update that releases around March and September, with an 18-month servicing period for each release. The Semi-Annual Channel replaces the Current Branch (CB) and Current Branch for Business (CBB) concepts starting with Windows 10, version 1703, which released for broad deployment on July 27, 2017. Windows Update for Business deferral policies based on broad deployment readiness should be calculated from that date.
With each Semi-Annual Channel release, we recommend beginning deployment right away to devices selected for early adoption (targeted validation) and ramp up to full deployment at your discretion, regardless of the "Targeted" designation. This will enable you to gain access to new features, experiences, and integrated security as soon as possible. For more information on servicing, see this IT Pro blog post and Quick guide to Windows as a service.
Please refer to Windows Official Website for Details.