I was wondering if it will be possible to edit the term “Sales invoice” and change it to just plain “Invoice”.
In my case, the term sales invoice is slightly misleading.
From Settings > Sales Invoice Template, you can Rename it to anything that you want. Same for Quotes.
Are you using Manager in English? When you create new invoice, it should just say “Invoice” by default. You can change this default by going to Sales Invoice Template section under Settings tab as suggested by @netspc.
Renaming a tab is not possible. You can translate a tab into another language but that’s something different. The reason why the tab is called “Sales Invoices” is because from your point of view, all invoices you issue to customers are called “Sales Invoices”. All invoices you receive from your suppliers are called “Purchase Invoices”.
So it is necessary to call the tab “Sales Invoices” and not just “Invoices” to prevent ambiguity.