שבת ראש חודש – At least twice each year, Shabbat coincides with Rosh Chodesh.1 When this occurs, a special maftir and haftarah are read in honor of Rosh Chodesh. The maftir, Bemidbar 28:9-5, concerns the special korbanot brought for Rosh Chodesh. The haftarah is Yeshayahu 66:1-24 (today in all nuschaot, with verse 66:23 customarily repeated at the end).
Not to be confused with Shabbat Machar Chodesh (which occurs the day before Rosh Chodesh) and Shabbat Mevarchim (which occurs when Rosh Chodesh falls during the week following), nor with Shabbat ha-Chodesh (which occurs on the Shabbat before Rosh Chodesh Nisan).