Single petition, also known as unilateral divorce petition, is a legal document filed by one spouse seeking a divorce without the agreement or consent of the other spouse. It is typically used when one spouse desires to end the marriage, but the other spouse is not willing to consent to the divorce or cannot be located.

There are various reasons why someone might need to file a single petition for divorce:

1.    Irreconcilable Differences: The marriage has broken down irreparably, making it impossible for the spouses to continue living together as a married couple, but one spouse is unwilling to agree to a divorce. 

2.    Abandonment: One spouse may have abandoned the other for a significant period, making it necessary for the abandoned spouse to seek a divorce.

3.    Adultery: If one spouse has committed adultery and the other wishes to end the marriage as a result, they may file a single petition for divorce.

4.    Unreasonable Behaviour: If one spouse's behaviour is unreasonable or intolerable to the point that it has caused irreparable damage to the marriage, the other spouse may seek a divorce through a single petition.

Ultimately, a single petition allows one spouse to seek a divorce unilaterally when the other spouse is unwilling or unable to agree to the dissolution of the marriage.