Aleatory: the values exchanged are unequal and depend on an uncertain event. One insured may receive far more than she paid in; another receives no claim payment at all.

Conditional: the insurer's duty to pay depends on conditions being met, such as a covered loss occurring and the insured doing what the policy requires, like giving notice of the loss.

Unilateral: only the insurer makes a legally enforceable promise. The insurer promises to pay covered losses, but the insured cannot be forced to keep paying premiums; if payment stops, coverage simply ends.

Contract of adhesion: one party, the insurer, writes all the wording, and the applicant can only accept it or decline it. That is why an ambiguity is generally resolved against the insurer. California Civil Code §1654 says uncertainty that remains is read most strongly against the party who caused it, which in a policy is normally the insurer.