EHIC stands for the European Health Insurance Card, and it replaced the old card which was called E111 in 2006.
The EHIC provides coverage in all of the European Economic areas including Switzerland, Norway, Iceland, and Liechtenstein. The card allows for healthcare that is provided at a reduced cost, or for free in some instances. Coverage is for treatment that is needed for you to continue your stay wherever you are, until the date of your planned return. You are covered for pre-existing conditions and for maternity care that is routine, with the stipulation that you are not going abroad to give birth.
Anyone who is British, or ordinarily a resident in the UK or Switzerland, is eligible for an EHIC. Application is done online and is free. If your nationality is other than those listed, but you can prove that your ordinary residence is in the UK, you will be eligible. You would need to show proof that you are ordinarily a resident of the U with your visa, a letter from your employer, or on an approved form. If you do live abroad, but receive a state pension from the UK, you may be eligible with the proper documentation.
Your partner and/or your children will all have to have separated cards and they will need to apply as well under the same rules.
The EHIC is not a substitute or an alternative for travel insurance, so when traveling it is important that you not only have the EHIC card, but to also have valid private travel insurance. There are insurers that do insist that you have an EHIC card, and many of those will waive any excess if that is the case.
The EHIC is a very convenient way to ensure that you will have adequate medical coverage when traveling in the prescribed countries, and that you will receive the best medical treatment.