In the context of how data are organized: A data collection is a logical grouping of (research) datasets that share a common aspect or concept. A data collection is the highest in the hierarchy of data groupings (data collection, dataset, row or record in a dataset). It comprises a grouping of datasets that have a strong connection and it is organised coherently around a single element or concept (e.g., model, instrument).
In the context of how data are collected, data collection is the process of creating, recording, acquiring, or linking to specified data or type of data. A description of this process includes specifying file formats, naming conventions, data structure, and what provisions have been made for version control, data re-use, sharing, and long-term access to the data.