Open Educational Content/olcos/Tutorial1 Use Open Content/searching in dedicated ODEC sites
Since there are also ODEC specific sites like preprint servers or learning object repositories search is also an important topic for these sites.
A repository is a central place where data is stored and maintained. A repository can be a place where multiple databases or files are located for distribution over a network, or a repository can be a location that is directly accessible to the user without having to travel across a network. [wikipedia]
Looking at educational repositories in the mean of being a resource for ODEC you will discover from whole courses to smaller learning objects a lot of valuable, reusable educational content for a variety of subjects. A repository supports mechanisms to import, export, identify, store and retrieve digital assets. Putting digital content into a repository enables staff and institutions to manage and preserve it, and therefore derive maximum value from it. Educational repositories mainly contain elearning objects and teaching materials or research data.
In the Wikipedia a learning object has been defined as the following:
• "Any entity, digital or non-digital, that may be used for learning, education or training" 
• "Any digital resource that can be reused to support learning" 
• "Web-based interactive chunks of e-learning designed to explain a stand-alone learning objective" 
All repositories offer their own search facilities. Additionally one can find search facilities providing federated search in different repositories (see Web Resources below). Try it with one repository and you will get an idea on how it works.
Selected Web Resources
Federated Search Facilities
Educational Material Server