Q: What does "raw data" exactly mean?

Raw data refers to data that has not been processed. Raw data needs to undergo processing such as selective extraction, organization, and sometimes analysis and formatting to make it presentable. The data that you have collected for the purpose of your research is raw data. It is also called primary or source data.

Most journals ask for a part of raw data, i.e., only the underlying data that is vital and relevant to the paper. This is a step which journals are taking in response to an increased call for transparency within the academic community. With a large number of papers being churned out every year by journals, new theories and findings are constantly being published. Accessibility of raw data ensures reproducibility of these findings and enables researchers to conduct replication studies. Accessibility of raw data is the right step towards open science as it ensures reproducibility of these findings. 

Generally, journals ask for raw data to be provided along with the manuscript as supplementary information, which is part of the submission package. You can look up the author information page of a journal to find out whether they require raw data at the time of submission. Some of the popular journals that ask for raw data are PLOS ONE, BioMed Central journals, The ISME Journal, and some of the Nature Publishing Group journals.