The closest proximity of letters, there being the intervention of half a mātrā or prosodial length between them, is called contact or saṃhitā,
When words are in sanhita, they are glued together by the rules of sandhi. As दद्ध्यत्र = दधि + अत्र.,
परः संनिकर्षः संहिता
Adhyāya 1 · Pāda 4 · Rule 109