This is the 228th most frequent French word.
prochain
Next.
Here, 'prochain' is used as an adjective meaning 'next', describing 'train'.
Le train prochain arrive dans 10 minutes.
The next train arrives in 10 minutes.
Here, 'prochaine' is used again in its feminine form, aligned with 'vie', to indicate 'next' in a sequence of lives.
Dans ma vie prochaine, je serai un artiste.
In my next life, I will be an artist.
In this case, 'prochaine' is the feminine form of 'prochain', agreeing with 'semaine', meaning 'next'.