Surveys are the individual questionnaires that you send to participants, which are created as forms in the Structure tab.
Survey packages act as digital folders for your surveys, and allow you to send them to an email address. Whether a package contains a single survey form or many, surveys are always sent via packages. You can learn how to create a survey package in the manual article - Create a new survey (package).
Survey package invitations are survey packages that are planned or instantly sent to a participant's email address. The data filled in by the participant will be contained in the relevant survey package invitation. You can learn how to create a survey invitation in the article - Send surveys
The survey package invitations are listed in the overview provided in the Surveys tab. The survey package you select when creating an invitation is what appears as survey 'name' for the participant. The individual surveys and steps are shown in the step navigator while answering a survey, if you have selected to display the step navigator when setting up the survey package.