Solemnity is the feminine noun that means the quality of what is solemn, emphatic and majestic.
In many cases, the word solemnity is synonymous with a ceremony that makes an event solemn, authentic and valid. These can be formalities that give importance to a particular event, such as the solemnity of possession of a person for a given public office. Ex: Thousands of people attended the ceremony of possession of the new Mayor.
Sometimes used in a more familiar way, it can mean emphasis or a deep voice. Ex: The father solemnly announced the punishment.
As it is a word closely related to ceremonies, it is often used in the case of religious celebrations accompanied by readings for liturgy. An example of this are Catholic ceremonies such as the Solemnity of the Ascension of the Lord, Solemnity of Pentecost, Solemnity of Corpus Christi or Solemnity of the Sacred Heart of Jesus.
graduation ceremony
The expression solemnity of graduation indicates a symbolic ceremony that takes place to celebrate the end of a stage of studies. There is a high school graduation ceremony, early childhood education, etc.
At these events, trainees often receive diplomas certifying the completion of the cycle in question and speeches are given by relevant people at graduation.
