अनिरुक्तस्त्रयोदशः स्तोभः संचरो हुंकारः ॥ १.१३.३ ॥
aniruktastrayodaśaḥ stobhaḥ saṃcaro huṃkāraḥ || 1.13.3 ||
3. The thirteenth stobha huṃ is not clearly defined. Various scholars have defined it in various ways. [Thus, it is up to people to meditate on it as they like.]
Sañcaraḥ, variously interpreted; aniruktaḥ, not clearly defined; trayodaśaḥ stobhaḥ, the thirteenth stobha; huṅkāraḥ, the syllable ‘huṃ’.
Earlier, twelve stobhas were explained along with how they could be used for meditation. Those stobhas are: hāu, hāi, atha, iha, ī, ū, e, auhoyi, hiṃ, svara, yā, and vāk. Now the thirteenth stobha, huṃ, is being discussed. The Upaniṣad says here, however, that no one knows for certain what huṃ means, so people are free to meditate on it as they please.