The concept of traditional ecological knowledge (TEK), along with synonymous or closely related terms like indigenous knowledge and native science, has some of its origins in literatures on international development and adaptive management. There is a tendency to want to determine one definition for TEK that can satisfy every stakeholder in every situation. Yet a scan of environmental science and policy literatures reveals there to be differences in definitions that make it difficult to form a consensus. What should be explored instead is the role that the concept of TEK plays in facilitating or discouraging cross-cultural and cross-situational collaboration among actors working for indigenous and non-indigenous institutions of environmental governance, such as tribal natural resources departments, federal agencies working with tribes, and co-management boards. This is a philosophical paper that explores how the concept of TEK is defined in science and policy literatures and what purpose it serves for improving cooperative environmental and natural resources stewardship and management between indigenous and non-indigenous institutions. The philosophical method applied here is one that outlines numerous possible meanings of a concept (TEK, in this paper) and the implications of each meaning for science and policy. In science and policy literatures, there are different definitions of TEK. Controversy can brew over TEK when people hold definitions that are based on different assumptions. There are two kinds of assumptions about the meaning of TEK. The first kind refers to assumptions about the mobilization of TEK, or what I call knowledge mobilization. The second kind involves assumptions about how to understand the relationship between TEK and disciplines like ecology or biology, or, in other words, the relation between TEK and science. Different positions that fall under the two kinds of assumptions (knowledge mobilization; TEK and science) can generate disagreements because they imply differences about “whose” definition of TEK gets privileged, who is counted as having expert authority over environmental governance issues, and how TEK should be factored into policy processes that already have a role for disciplines like forestry or toxicology in them. In light such disagreements, I argue that the concept of TEK should be understood as a collaborative concept. It serves to invite diverse populations to continually learn from one another about how each approaches the very question of “knowledge” in the first place, and how these different approaches can be blended to better steward natural resources and adapt to climate change. The implication is that environmental scientists and policy professionals, indigenous and non-indigenous, should not be in the business of creating definitions of TEK. Instead, they should focus more on creating long term processes that allow the different implications of approaches to knowledge in relation to stewardship goals to be responsibly thought through.