In Islamic literature, Ilhaam (إلهام) is a type of inspiration or revelation from Allah which does not necessitate prophethood for the recipient. It is generally understood as a strong intuition or inclination. An example from the Qur'an is in Surah al-Shams verse 8. When Wahi (وحى) is used for non-prophets, it is understood as Ilhaam.
According to Sufi tradition, which is prevalent in the region that Ahmadiyya was born, it is understood as a type of non-prophetic revelation given to extremely righteous people, providing them with deep spiritual insight and divine secrets.
Mirza Ghulam Ahmad claimed to have received thousands of such messages from God, ranging from the mundane to Quranic verses. The latter were verbatim or with slight modifications. He did not have any hesitation in publishing these messages, his visions and dreams in his books, advertisements or periodicals.
The Qadiani Ahmadiyya have compiled all these into a book that is available in Urdu as well as English, called Tadhkirah.