Read the following passage carefully and answer the question that follows.

When offices reopened after the pandemic, many companies expected employees to return full-time. Instead, a hybrid pattern emerged: workers split their week between home and office. Surveys across Indian IT firms suggest that employees value the commute time saved more than any other benefit, while managers worry about weaker mentoring for junior staff. Some firms have responded by designating 'anchor days' - fixed days when an entire team is present - so that collaboration and training are concentrated rather than scattered. Early evidence indicates that this compromise preserves most of the productivity gains of remote work while restoring some of the informal learning that new employees miss. The debate is no longer about whether hybrid work will last, but about how to structure it well.

In the passage, 'anchor days' refers to