Strategic Assets is a concept defined within ITIL version 3 that relates to the basic premise of business customers wanting the outcomes associated with owning assets such as hardware, software, staff, infrastructure, BUT they don't want the associated risk of supporting, managing, maintaining those assets.
Of course, within the modern day business organization, we have IT departments that take ownership of the risk of managing the strategic assets on behalf of the customer under a given set of agreed upon conditions (e.g. financial, control). These conditions are typically documented in a Service Level Agreement (SLA).
Perhaps an easier to comprehend explaination of strategic assets comes from understanding that strategic assets are NOT the traditional assets of an organization. Not the computer infrastructure, not the trucks in a transport company.
Strategic assets is what we have when we take these traditional assets (resources) and combine them with unique capabilities of people and the result is a distinctive advantage for the company or a ability to perform at a level that exceeds the competition.