Kala Sarpa Yoga is said to be formed when all seven of the classical planets fall between Rahu and Ketu, the lunar nodes, so that the whole chart is enclosed within the nodal axis. It is presented in modern Indian astrological literature as a serious affliction bringing obstruction and struggle, and a considerable trade in remedial ritual has grown up around it.
The dating matters. This configuration is not treated as a named yoga in the classical texts: Brihat Parashara Hora Shastra describes a Sarpa Yoga formed by malefics occupying the three angles, which is a different thing, and the nodal-enclosure yoga under this name appears in twentieth-century compilations and popular manuals rather than in the classical corpus. Many experienced practitioners treat it as a pattern to be noted rather than as a verdict, and some reject it outright. Anyone told they have it is entitled to know that its pedigree is modern and contested.