A file that contains many JSON, what is the definition of such file?
It's a JSON Lines text file format : http://jsonlines.org/
JSON Lines text format, also called newline-delimited JSON. JSON Lines is a convenient format for storing structured data that may be processed one record at a time. It works well with unix-style text processing tools and shell pipelines. It's a great format for log files. It's also a flexible format for passing messages between cooperating processes.