Good definition of corporate culture from Innovation Excellence:
"Corporate culture is the set of assumptions, beliefs, practices, formal and informal rules and attitudes about how a company operates. Corporate culture evolves over time, and is both formal and informal. Corporate culture often shifts over time as well. Young entrepreneurial firms and startups have a culture that thrives on risk, speed and change. Growth is paramount. Older, established firms have a culture more typically based on rules, hierarchy, achievement of predictable milestones. While many firms have elaborately detailed organizational hierarchies and established workflows, corporate culture is often much more informal, and more powerful than any individual, and often more powerful than senior executives appreciate or expect.
"In an organization with a strong corporate culture, people learn to fit in quickly, adjust their thinking to the predominant culture or are quickly ostracized. Corporate culture, more than any other factor, details how people think, what they believe is important and valuable, and dictates how work should get done. It is difficult to change, especially under duress, and often communicates much about the values and intentions of a business."