A commission is a formal document issued to appoint a named person to high office or as a commissioned officer in a territory's armed forces.
Commissions are typically issued in the name of or signed by the Head of State. In Commonwealth realms other than the United Kingdom, they may be signed by the Governor-General, the representative of the Monarch of the United Kingdom, who is also Commander-in-Chief in and over that realm.
Because the word "commission" can also refer generally to an individual's duty, the more specific terms commissioning parchment or commissioning scroll are often used to specify the commissioning document. However the document is not usually in the form of a scroll and is more often printed on paper instead of parchment. In Canada, there is a differentiation in terminology according to rank; officers are accorded commissioning scripts whereas Chief Warrant Officers are accorded scrolls.
Here is an example from Canada:
ELIZABETH THE SECOND, by the Grace of God of the United Kingdom, Canada and Her other Realms and Territories Queen, Head of the Commonwealth, Defender of the Faith
To ........ .........
hereby appointed an Officer in Her Majesty's Canadian Armed Forces
With Seniority of the .... day of ......... ....
WE reposing especial Trust and Confidence in your Loyalty, Courage and Integrity do by these Presents Constitute and Appoint you to be an Officer in our Canadian Armed Forces. You are therefore carefully and diligently to discharge your Duty as such in the Rank of .............. or in such other Rank as We may from time to time hereafter be pleased to promote or appoint you to, and you are in such manner and on such occasions as may be prescribed by us to exercise and well discipline both the Inferior Officers and Non-Commissioned Members serving under you and use your best endeavour to keep them in good Order and Discipline, and We do hereby Command them to Obey you as their Superior Officer, and you to observe and follow such Orders and Directions as from time to time you shall receive from Us, or any other your Superior Officer according to Law, in pursuance of the Trust hereby Reposed in you.