Hi,
The issuance of share certificate whether in the case of a privately or publicly held company the governing provisions and rules are under Section 46(3) of the Companies Act, 2013 and Rule 5(2) of the Companies (Share Capital and Debentures) Rules 2014.
The share certificate should be issued in Form SH-1 or any document that resembles Form SH-1:
Name of the Company
CIN Number of the Company
Registered Office of the Company
Name of the owners of the shares
Folio number of the member
Number of shares represented by the share certificate
Amount paid on the shares
Distinctive number of shares
Number of share certificate
Answering to your query, although the Companies Act, 2013 is silent on the term 'folio' but in short folio number of a shareholder or member of a company can be termed as a number of the page of the shareholder’s register on which details of a shareholder is recorded.
Lastly, if your company has two promoter shareholders A and B as a subscriber to the memorandum of association, you can assign them folio numbers 1 and 2. For every new subscriber you can accordingly assign the numbers. If there are joint-holding by two or more exiting subscribers, you can assign different folio numbers. Similarly, in the case of HUF etc., you can assign different ones. There is no as such any regulation on assigning the folio numbers to the members. You can therefore have the creative freedom to assign folio numbers to the shareholders.
You refer to the attached file containing the Form SH-1 which shows the sample format of the share certificate.
Hope my answer provides some idea.