• It is the family of printing and printmaking techniques in which the image is incised into a surface and the incised line or sunken area holds the ink. 
• It is the direct opposite of a relief print.
• Normally, copper or zinc plates are used as a surface or matrix, and the incisions are created by etching, engraving, drypoint, aquatint or mezzotint. 
• Collagraphs may also be printed as intaglio plates. At one time intaglio printing was used for all mass-printed materials including banknotes, stock certificates, newspapers and magazines, fabrics, wallpapers and sheet music.
• Today intaglio engraving is largely used for paper or plastic currency, banknotes, passports and occasionally for high-value postage stamps.
• The appearance of engraving is sometimes mimicked for items such as wedding invitations by producing an embossment around lettering printed by another process (such as lithography or offset) to suggest the edges of an engraving plate.

In news:

• The Delhi High Court on Wednesday suggested to the Centre and the Reserve Bank of India to examine the new ₹50 notes, which allegedly were “very difficult for visually impaired person to identify”.
• The old ₹50 notes had a square intaglio print, which could be felt by touch, and helped the visually impaired identify the denomination. However, the new note does not have such identification marks.
• The High Court had during the previous hearing declined to stay the printing and circulation of the new ₹50 notes, issued on August 18. The RBI has kept a special feature in intaglio on all notes except the ₹10 note.
• This feature is in different shapes for various denominational.

Source: Wiki & TH