Strengths are the positive possibilities (risks) that may arise from within the project's organization. For instance, a related activity may result in deliverables that can be re-used and reduce the projects' cost and time for certain activities.
Weaknesses are the possible negative things that come from within the project's organization.
Opportunities are positive situations coming from outside the project's organization.
Threats are negative possibilities based on external circumstances. For instance possible delays caused by unseasonable weather or new legal regulation would be threats.