Tāṃ is the seed syllable of the Tārā's, being the first syllable of their name plus the anusvāra.

There is an interesting relationship between the body of White Tārā, and the form of the tāṃ in the Siddhaṃ script which you can read about on White Tara, tāṃ, and the Mandala.

Other bījas:   a | āḥ | dhīḥ | hūṃ | hrīḥ | maiṃ | oṃ | traṃ | phaṭ | svāhā |

Examples

the seed syllable tam
Siddhaṃ
tam seed syllable
Tibetan - Uchen
(from Rivendell Retreat Centre)